In Scott McPherson’s new play at Playwrights Horizons in New York, test results are never good news. Bessie (Laura Esterman), 40 years old and single, isn’t exhausted just because she’s spent most of her life caring for her father, a bedridden stroke victim who can’t speak and whore only pleasure is seeing the bobbing patterns of light made by flicking a mirror. “Dad’s been dying for about 20 years. He’s doing it real slow, so I don’t miss anything,” says Bessie, matter-of-factly. Or because her her sweetly dippy Aunt Ruth (Alice Drummond), who has a bad back and wears a biofeedback device that sets off the automatic garage-door opener. No, things get worse: Bessie is diagnosed with leukemia. Her only hope is a bone-marrow transplant, so her estranged sister, Lee (Lisa Emery), turns up as a potential donor along with Lee’s two sons-one of whom has been in a mental hospital because he burned down their house. Talk about a dysfunctional family.

“Marvin’s Room” has a wonderful cast, who steer the play as it veers between sadness and whimsy, agony and irony. The tone keeps shifting, but never becomes maudlin or saccharine-tough to pull off because Bessie is a saint. “I just did what anyone would do,” she protests. “I can’t imagine a better way to have spent my life.” As the play’s anchor, Esterman gives Bessie a radiant, loopy charm. She is the madonna; her sister Lee the slutty, bitter divorcee in tight pants. Bessie knows how to win over Hank (Mark Rosenthal), Lee’s angry adolescent arsonist son, who wears a T shirt with a happy face that’s been shot in the forehead. Lee, on the other hand, parcels out love to Hank as frugally as she offers him M&Ms-*ne by one. In this household, it’s clearly the healthy people who need a spiritual cure. Director David Petrarca keeps the tight scenes moving: some are darkly comic, many are painful and occasionally one of them-such as Bessie’s tale of her one true love-doesn’t quite ring true.

This is the second full-length play by the talented 32-year-old McPherson. It was first performed in Chicago, where he lives, and the Seattle Repertory Theatre plans to stage a production in late January. In a program note, the playwright writes about how he grew up with a grandmother bedridden by cancer and took it in stride. He also writes that his lover is ill with AIDS; and he has suffered from AIDS-related illnesses as well. Though “Marvin’s Room” could be taken as a metaphor for coping with AIDS, it is far more universal. Anyone who has been on the dark side of the looking glass of chronic illness will recognize the touchstones, even the absurd ones. But more than that, the play is about choosing a life. “I’ve had such love in my life,” says Bessie of her invalid father and aunt. “I mean-I love them. " When Bessie’s blood tests come back, that love can’t take away her fear. But it makes her feel more satisfaction than self-pity.