Pegasus Players, the popular non-Equity company in Chicago that offered the American premiere of Stephen Sondheim's Saturday Night in 1999, opens the world premiere of the musical, Muscle, by James Lapine, composer William Finn and lyricist Ellen Fitzhugh, June 13.

The full-length tuner, once a project being developed by Lapine and Stephen Sondheim, began previews June 5 and continues to July 22. Gareth Hendee directs the new piece, which concerns an intellectual named Max Riddle who gives up his academic career and becomes obsessed with bodybuilding. Previously, in a one act form, a Lapine-Sondheim treatment of Muscle (based on Samuel Fussel's book of the same name) was once going to be paired with the one-act musical, Passion, also by Sondheim and Lapine. When Passion became a full-length piece, Muscle was pulled and not flexed again by those collaborators.

Pegasus executive director Arlene Crewdson said she received a call from Lapine in 2000, inquiring about premiering the show at her theatre, and she embraced the idea. Lapine is the Pulitzer Prize-winning librettist and director of Sunday in the Park With George, Passion and Into the Woods.

Crewdson said Lapine heard of Pegasus from Sondheim, who was in residence with Pegasus when Saturday Night was being honed (orchestrator Jonathan Tunick, a Finn collaborator, also worked with Pegasus).

For Muscle, Jon Steinhagen musical directs a cast of 17, including Jane Blass, Rob Hancock (as Max), Anita Hoffman, Corey James, Timothy Jon, Chuck Karvelas, Dan Loftus, Carrie McNulty, Henry Odum, Brad Potts, Chavez Ravine, Michael Reyes, Eddie Schumacher, Kate Staiger, Joel Sutliffe, Megan Van De Hay and Audrey Yeck. The creative team includes James Bagnell (assistant director), Ann Filmer (choreographer), David Lander (lighting designer), Jack Magaw (set designer), Steve Mezger (sound designer) and Nan Zabriske (costume designer).

Sondheim's Saturday Night, a 1954 script that emerged in the 1990s, subsequently had a 1999 winter-spring run in New York City at Off-Broadway's Second Stage (followed by a New York cast album). Presumably, if the creators feel it's ready and a producer gets attached, the show will get a major Equity staging somewhere. The writers were in attendance during the rehearsal process twice.

Lapine and Finn collaborated on the Tony Award-winning Falsettos and Off-Broadway's A New Brain. Ellen Fitzhugh's lyrics have been heard in the 1985 Broadway musical, Grind, and Off-Broadway's Diamonds and the developing Paper Moon, which played Paper Mill Playhouse in 1993.

The staging of Saturday Night in 1999 was a "boon to our reputation," said Pegasus's Crewdson. Director Gareth Hendee has worked with Lapine on a dozen productions, and served as associate director of Dirty Blonde on Broadway and in San Francisco. He staged Dahling — the Life and Times of Tallulah Bankhead Off-Broadway in 2000.

Pegasus Players is at 1145 W. Wilson Ave., at the O'Rourke Center on the campus of Truman College. Tickets are $20-$25. For information about Pegasus Players, call (773) 878 9761.

— By Kenneth Jones