Kellie Waymire, a popular young actress who earned critical praise for her performance as a dog in A.R. Gurney’s offbeat play Sylvia and appeared frequently on television series from Friends to Six Feet Under, has died. She was 36.

Ms. Waymire died Nov. 13 at her home in Venice, Calif., apparently of an undiagnosed medical problem, said her agent, Billy Miller. He said an autopsy would determine the specific cause of death.

A familiar face on television for the past decade, Ms. Waymire came into her own critically in 1996 when she became the lovable dog Sylvia — a part handled by Sarah Jessica Parker when the Gurney play made its debut off-Broadway a year earlier — at San Diego’s Old Globe Theater.

The role won Ms. Waymire a Drama-Logue Award for outstanding performance.

Ms. Waymire appeared in a revival of Noel Coward’s Present Laughter at the Pasadena Playhouse in 1998, again winning critical praise.

She also appeared at Los Angeles theaters in recent years in the plays On the Jump and in Arthur Miller’s The Man Who Had All the Luck.

The actress was a regular in respected regional theaters around the country — not only Old Globe and Pasadena Playhouse, but also South Coast Repertory, La Jolla Playhouse, Circle X Theatre and Antaeus Company in Los Angeles, Seattle Repertory Theater, Milwaukee Repertory and the Rogue Theatre in New York City.

Born July 27, 1967, in Columbus, Ohio, Ms. Waymire graduated in acting and won the Greer Garson Award at Southern Methodist University, then earned a master of fine arts from the University of California, San Diego.

She began her career in New York on the soap opera One Life to Live. After moving to Los Angeles, she appeared in episodes of Seinfeld, Ally McBeal, The Practice, Judging Amy, The X-Files, Wolf Lake, Star Trek: Voyager and Star Trek: Enterprise.

Most recently, she appeared on a Friends episode telecast Oct. 3, and was the spunky wife opposite Dylan Baker on Fox’s haunted family The Pitts. She also appeared last year in the recurring role of Melissa the prostitute in the cable series about undertaking, Six Feet Under.

She is survived by her parents, Jack Waymire and Vicki Currant; brother and sister, Tony Currant and Rebecca Cornwell, and her partner, Gary Judson Smoot.