I see your hippopotomonstrosesquipedalianism and raise you a ribulosebisphosphatecarboxylaseoxygenase

I suspect the organic chemists will win this one: they've got that verbal heritage from the nineteenth century, when their profession was essentially monopolized by the Germans. Modern IUPAC nomenclature retains the Germanic habit of building long words out of small segments with little in the way of spacing to leaven them, and even dashes only enter the picture because numbers get involved: 2,5-dimethoxy-4-bromophenethylamine, indeed. Physics people like me find "supersymmetry" a mouthful and crunch it down to "SUSY".

Blake--The chemists may win on paper, but what about on the tongue?

Transesterification.

Bremsstrahlung.

The more time passes the more I lament the fact that the field of psychoneuroendocrinoimmunology never really took off.

I'm a lawyer,not a scientist, but I handled a series of cases involving misdiagnosis of San Joaquin Valley fever.

After a while, "coccididiomycosis," "blastomycosis," and "histoplasmosis" all easily rolled off our tongues, much to the dismay of court reporters.

I'm sure coccididiomycosis would easily be beaten by scientists who get to practice on long words every day.

Immunohistochemistry.

I'm a grad student in organic chemistry, and I'll back up Blake's conjecture. Talking among other organic chemists, there are some things (mostly basic, well-known compounds) that get shortened - hexamethylphosphoramide becomes HMPA, tert-butyldimethylsilyl becomes TBDMS.

More often, though, you've got to use the whole word to assure that what you're trying to say is understandable, as backwards as it may sound. "OP AChE inhibitors" may be meaningless, but a decent chemist could probably accurately guess what "organophosphate acetylcholinesterase inhibitors" look like and do. Also as Blake pointed out, compound names can get unwieldy fast, but using the standard nomenclature is still better than saying "that one with the six membered ring, three bromines, and an alcohol group."

Here's some you hear often around my lab:

Anti-Markownikoff
Heterobimetallic
Tetraarylboronate
Hyperphosphorylation

If ones that include two words count, I'll throw in

Supramolecular assembly

and

Dipolar cycloadditions

I regularly use terms like "pseudogenization" and "rediploidization" and "endopolyploidy".

During grad school, the chair of our department studied coccididiomycosis, so yeah, that one's old hat to me. There are a lot of areas in epidemiology that end up with prefixes that make them ungodly cumbersome. (Technically, I suppose I could call my own area molecuinfectoepidemiology, if people can coin terms like "infectobesity," right?)

But for words that already exist, in my own field, how about anthropozoonosis? Not to be confused, of course, with zooanthroponosis...

I'm afraid the only long word I use semi-regularly is Schadenfreude. (make of that what you will :)
There are short nicknames for most insects with long scientific or proper names.

And how odd you posted this the same day I was blogging about Hot for words.

I just quickly searched my Word custom dictionary with perl for the longest word and found coimmunoprecipitation. I don't do much of it, but other people in the lab do. At 22 letters it's pretty long.

Oh, the perl command (if it will be any use to anyone) was:

perl -ne '$word = $_ if (length $_ > length $word); END {print $word}' Custom\ Dictionary

Clearly the neuropsychopharmacologists have no problem throwing around 26-letter words. But I guess they better make way for the psychoneuroendocrinoimmunologists.

Now that I think about it, physics and math pack a lot of meaning into people's names. We've got stuff named for Euler and Gauss, and things which Euler or Gauss discovered first but which we named for other people because Euler and Gauss already had so much, and we've got lots of hyphenated descriptors. Just yesterday I was proving a theorem with the Laplace-Runge-Lenz vector, for example.

The winner, in my experience, is the BBGKY hierarchy, a long series of equations which occurs in statistical mechanics. "BBGKY" expands out to Bogoliubov-Born-Green-Kirkwood-Yvon.

The neuropsychopharmacologists may need long business cards, but they don't name things after people called Bogoliubov.

Oddly enough... it was ribulosebisphosphatecarboxylaseoxygenase.

This lovely hexadecameric protein played a major role in my MS thesis.

It's not that rare. In fact it is the most common protein in the world. Really.

(Mostly because it's terribly inefficient.)

Shouldn't you be looking at the number of syllables rather than the number of letters in the word since you asked for "the longest word [one] would actually use in conversation" rather than in writing?

MikeG [15] Did you ever actually say "ribulosebisphosphatecarboxylaseoxygenase"? Or just rubisco?

On the 1978 album Motor Booty Affair by Parliament, there's a track called Aqua Boogie (a Psychoalphadiscobetabioaquadoloop).

As pointed out before, COIMMUNOPRECIPITATION is used commonly in biochemistry and cell biology.

Not as long but nice mouthfuls:
Monoubiquitinylation
Decapentaplegic
SonicHedgehog

If we're not exclusively into nouns, I'd say one of the most commonly used words in biochemistry papers, "spectrophotometrically" wins so far on a technicality. Then again, we never really speak this much in the lab. I think scientists just don't like tying their tongues in knots just to get a simple point across. So, rather than asking your undergrad minion to "be so kind as to analyze the sample spectrophotometrically", you tell them to "spec that crap." They get it, everyone's happy.

As Harrison Ford once said to George Lucas: "George, you can write this sh*t, but you can't SAY this sh*t." Amen.

I could use my native Swedish, but that'd be cheating I think; we have a completely different tolerance for long words, and some quite complex ideas are routinely expressed as one word. "capital gain tax", for instance is "realisationsvinstbeskattning" (28 letters, and yes, you'd use it in spoken conversation (if you're the kind of person to talk about capital gain taxes with people, of course)). Or "Nurse training course" is "sjuksköterskeutbildning" with 22 letters. There's many others.

In neurology you have some pretty long anatomical names. But it seems there's a natural cutoff at around 16-18 letters, or 8 syllables (which seems to be the determinant): "hyperpolarization", "paleospinothalamic", "intermediolateral". Longer than that and people have the sense to cut it up into several words, like "lateral geniculate nucleus", or shorten it into an abbreviation (for most neurotransmitters, for instance).

Any computer scientist should be familiar with "nondeterministically" (20 letters). And it's not too hard to pronounce. :)

Hmm... I must think hard to get past it...

Carl,
I had to say it a few times, but I added the 1, 5 between the ribulose and the rest of the mess. Which, I guess makes it ribuloseonefivebisphosphatecarboxylaseoxygenase.

You have to be careful where you leave your phosphates.

Most of the time, though, it was RuBisCO, or, since I was working with the gene for the large subunit, rbcL.

I forgot the most tongue twisting one that I have had to actually say:
hexanoyloxyfucoxanthins

And people wonder why I got away from studying dinoflagellates...

methylenetetrahydropholatereductase

I'm far from being science-literate, but I do try, in my own shabby way. I used to work as a purchasing clerk for a manufacturer of 'nutritional supplements' and I was the only person in the building who could pronounce 'polyenylphosphatidylcholine'; does that count?

These words have a strong internal grammar. I'm not sure they qualify as single words in the normal sense. It's more like Inuit than English.

I'd like to see a contest for the longest non-agglutinative word. Nondeterministically is pretty good (depending on where you draw that line)

Chemical nomenclature will, as Carl notes, get you into huge words very quickly, although they're generally broken up with hyphens and the like.

But here are some of the words that I say in the lab without even thinking about it: nucleophilicity, enantiospecifically, diastereoselectivity (a good solid ten syllables there), exothermically, hydrophobicity, Antimarkovnikov (that one often is written with a hyphen and includes a proper name, so perhaps it shouldn't count), levorotatory, polyheteronuclear, stoichiometrically, regioselectivity, etc.

And there are a number of biological terms that I've said from time to time, but which don't come up very often, like mucopolysaccharides or diacylglycerolacyltransferase.

But when it comes to chemical names, well, even without resorting to hyphens I can think of some that I've used more times than I can count: dichlorodicyanoquinone, hexamethyldisilazane, diphenylphosphoranylferrocene, hexamethylphosphoramide, tetramethylethylenediamine, and so on, and on. And while I have said all these at their full length, they're more commonly referred to as DDQ, HMDS, DPPF, HMPA, and TMEDA, for obvious reasons.

Yeah, I guess the chemicals are cheating.
In our lab we use the abbreviations anyway: SDS, EDTA, etc.

The rest is referred to as methyl-ethyl-badsh*t

Beaten already by Mike G, but I have another 20-letter one: "nondeterministically". (CS majors get big words too!)

22 letters & eminently pronoucable: neuropsychopharmacology. Not bad. And a hip field. love&evolution, drBluz

"Humans are merely and obviously aquaterrestuarborealistically adapted from a more primitive (in the scientific sense) basal primate" a naturalist might say, though I don't recall having heard it...nor have I had the situation to use it to advantage quite yet.

dimethyllysergicacid

antiestablishmentarian

Stoichiometrically and nondeterministically are good words, because they're formed like real words, and they refer to significant things with pretty broad application, and one of them can be figured out by a normal person without specialized training.

But I'm fond of paradimethylaminobenzaldehyde, with a tale of which I indoctrinated my kids on a longish car ride. The story is from Isaac Asimov, who related that someone during his student days called the compound to his attention, noting that it rolls so trippingly off the tongue that one can sing it. To the tune of the Irish Washerwoman.

Asimov said it became something of an obsession for a time, and he would unconsciously be humming or muttering it under his breath. On one occasion, he was hanging out in a dentist's waiting room, and the receptionist commented brightly that it must be fun to be able to sing it in the original Gaelic.

From there he went on to write of chemical nomenclature, in an article titled "How to Speak Gaelic". But hum a few bars sometime, and you'll see how well it fits. For variety, as he also suggested, you could do a bit of "This is the forest primeval, the murmuring pines and the hemlocks..." But does anyone know even that much of Evangeline today?

No! Even if you use the long form of RuBisCO, it's not one word, it's three:

Ribulose-1,5-bisphosphate carboxylase/oxygenase

you don't get to just merge words as if it's German, as in Rindfleischetikettierungsüberwachungsaufgabenübertragungsgesetz (63)

Those umlauted u's showed up properly in the preview.. :(

Porlock Junior: John A. Carroll was so inspired by Asimov's love of "paradimethylaminobenzaldehyde" that he wrote "The Chemist's Drinking Song" based on the word (to the tune of "The Irish Washerwoman"). Lyrics can be found here.

Thanks, Jim.
Stealing all my fun... :-p

The scientific name for black lung disease is [i have to insert spaces in this single unbroken word to avoid an error in the form submission system] pneumo ultra microscopic silico volcano conio sis spelt P-N-E-U-M-O-U-L-T-R-A-M-I-C-R-O-S-C-O-P-I-C-S-I-L-I-C-O-V-O-L-C-A-N-O-C-O-N-I-O-S-I-S. caused by the inhalation of coal dust, characterized by formation of nodular fibrotic changes in lungs."

I used to say a a good number of longer chemical names out loud frequently, especially when the preferred abbreviation is also commonly used elsewhere. For example, I normally say hexamethylenetetramine since I associate HT with hydroxytryptamines (particularly 5-HT).

The longest one I came up with is quite short in this company: haploinsufficiency, but we throw it around the lab a lot.

Also, practicing scientists often make nouns of verbs and vice versa. For example, we say "homozygose", not a word, instead of "make homozygous", which takes longer to say.
(An example: "Did you manage to homozygose that mutation?")

When i let slip some really long word, someone nearby will often say "bless you", because, clearly, i've just sneezed. I doubt i'd break any records here. But if my vocabulary is too copious for your diminutive comprehensibility, i will endeavor to elucidate more explicitly. (A classic in 4th grade, anyway.)

Heh, Worm_Guy, you just made me remember an old joke...

What does the H. stand for in Jesus H. Christ?

Haploid.

Heh.

Not that long, but trinitrotoluene does have a certain bang to it.

Those of us dealing with dinosaurs have had the pleasure in recent years to throw around words like "infrapostzygapophyseal" and "centroprezygapophyseal" (technically not the correct names for the structures they describe, but...). And we vertebrate paleontologists get lovely scientific names, too, like Micropachycephalosaurus, Opisthocoelicaudia, Chometokadmon, Kallikobotion, and Huehuecuetzpalli.

In a broader realm, evolutionary scientists get frabjuous words like "autapomorphically" and "paleobiogeographically," which get used on a regular basis.

afterhyperpolarization
22 letters

neuropsychopharmacology 23 letters.

today in school i suggested pneumonoultramicroscopicsilicovolcaniconiousis as a spelling word on our test. (and yes, i can say and spell it off the top of my head.)it has 46 letters and 19 syllables. it is the medical term for lung cancer. i am 13, the bigger the words, the beter. email me at sk8aja@yahoo.com if you have a longer one for me.
Good luck not getting your tongue tied!

Antidisestablishmentariansim. 28 letters