Monteith & Rand do their best work seat-of-the-pants, with the audience their willing accomplice.

In their act at Arena's Kreeger Theater, the comedy team makes up songs on the spot out of silly phrases supplied by you; they depend on you for sound effects when they do a murder mystery; they improvise scenes, according to situations you provide, in a series of styles that you have ordered up: maybe soap opera to start, followed by grand opera and Tennessee Williams, then "Mr. Rogers' Neighborhood," topped by Busby Berkeley and Shakespeare.

And, while engaged in such side-splitting labor, they manage to give the impression that they're having a good time.

John Monteith is a friendly-looking fellow with a comfy paunch and a reassuring smile. Suzanne Rand is a svelte strawberry blond whose flexible face can change instantly from pretty to crazed. Both are goose-loose performers, lightning fast on their feet, with a bent for the ribald, wicked, stupid and just plain weird.

Much of the time -- but depending on the crowd, the atmosphere and the fickle gods of comedy -- they're very funny, making you laugh now and then till it hurts.

That's true of their scripted sketches -- in which they can capture, for instance, the excruciating awkwardness of a singles-bar chat -- but it's even more true when they wing it.

The audience, of course, plays a crucial role. I wish the crowd at the Kreeger the other night had been more attentive and perhaps less rowdy than they were. Too often, some of the suggestion-shouters stepped on Monteith & Rand's improvisations, and a person in the balcony actually asked them to do a routine using a Korean Air Lines pilot. "Oh no," Rand said, smiling weakly and shaking her head. But they rolled with the punches like the troupers they are, and I found myself giggling more often than not.

MONTEITH & RAND -- At the Kreeger through October 9.