The Kronos String Quartet and the Modern Jazz Quartet are a musical disparity. The former is a self-described "experimental string quartet" that takes all sorts of music -- from native African to psychedelic American -- and twists it into a unique, orchestral sound. The latter is a "chamber jazz" ensemble that in 38 years has created a smooth, cool sound that has made the players legendary and influential.

What the two have in common is their approach -- there are no boundaries in their music. Their philosophy is that string quartets don't always have to play 18th-century European compositions and jazz quartets don't always have to do American '40s standards.

"Exploring, that's what we do," says Kronos founder David Harrington, "but beyond exploring, it's discovery. It's becoming a whole world of possibilities in quartet music."

Back in 1981 at the Monterey Jazz Festival, the Kronos premiered a work written for it by the Modern Jazz Quartet's musical director and pianist, John Lewis. That was the beginning of a symbiotic relationship that has brought the two groups together over and over again. They have toured together periodically, and Lewis has continued to compose pieces that the MJQ and Kronos perform together, including "Three Windows" and "Alexander's Fugue" (which Lewis describes as "contrapuntal piece") and "Piece" ("which was written and recorded a long, long time ago," he says).

The Kronos String Quartet and the Modern Jazz Quartet will perform at Wolf Trap tomorrow night at 8. Tickets are $13 and $20 and available at TicketCenter or by calling 432-0200.