I just came across a 6-voice fugue in the "Symphonic Variations and Sonata on a Palestinian Theme" Op. 39 by Joseph Achron.

That may be the 'biggest' fugue I've seen -- I think the biggest in Bach's WTC are 5-voice... that's a lot of voices to control at one time!

What's the biggest fugue you've seen/heard/played?

I've never done more than 1-voice.

Not the WTC, but the second ricercar in Bach's Musical Offering (the one Webern orchestrated) is also a six-part fugue.

There's a pretty massive fugue in the development section of the first movement of Mahler's Eighth Symphony. I haven't counted the number of contrapuntal parts, but I'm pretty sure there are at least six -- it is the "Symphony of a Thousand" after all...

Not quite a fugue (though containing a good amount of imitation), but there's always Tallis's fourty-part motet Spem in alium.

Edit: On a similar scale, there's Biber's Missa Salisburgensis for 53 independent instrumental and vocal parts.

I've played a 4-voice fugue.

I'm learning a 4-voiced fugue for an audition piece.

The biggest I'm aware of is the 6-voice ricercare that Janus mentioned. As for playing, I've done about 3/4 of the WTC book one, so plenty of 4-voice fugues. I have played around with the c# minor fugue (5 voices), but never studied it up to mastery. Maybe I'll take that one on seriously - it's such a fantastic fugue - a 5-voice triple fugue...

I thought the last movement of Barbers piano sonata consisted of a pretty gargantuan fugue....

Alkan's Grande Sonata has a fugue for 8 voices. It's borderline cacophony, but somehow he makes it work.

The fugue in the Liszt sonata is tricky to perform, especially since there's NO WAY OUT if you have a memory lapse.

Which Helmut Walcha arranged for organ. Very, very difficult.

And no, I've never attempted to play it.

Actually nine voices should one choose to take into account the doubling.

I certainly understand your observation about the Liszt Sonata. I once heard a student come to grief in that fugue. Complete memory loss, I felt very sorry for his predicament.

The Liszt remains a very "sacred" piece of music to me -along with the Beethoven Op 111, Bruckner's 8th, Beethoven's 9th, Elgar's Gerontius- to this day I've never read through the Liszt from beginning to end. It is too daunting for me to even consider. And of course it helps not that Argerich "swallowed it whole". Say what you will about that white hot recording -and it is a classic- but I've never really figured out how she does it.

So "argerichfan", i am a newbie to martha (but I am only 14, almost). I find her playing completely amazing and I have recently discovered her Utube clips !!..I am hoping to see her live at Carnegie Hall later this year. I have tried to read about her but there is no "authorized biography" so to say.. just snippets.. watched the interview bits on UT.. Of course I could be missing something obvious.. but even her background such as her teachers seems a bit here and there (?Michelangeli? how come she did not get too much into Debussy?)..
It feels as if there is some controversial opinions also about her artistry. She also does not seem to have too many recordings considering she is almost 70 (right?).. I bet you know quite a bit about her.. I could not ask you to pray tell, but may be indicate some sources for the novice?..
Thanks