Dreyfuss began acting in his youth, at Temple Emanuel of Beverly Hills Arts Center and Westside Jewish Community Center, under drama Teacher Bill Miller. He debuted in the TV production In Mama's House, when he was fifteen. He attended San Fernando Valley State College, now California State University, Northridge, for a year, and was a conscientious objector during the Vietnam War, working in alternate Service for two years, as a clerk in a Los Angeles hospital. During this time, he acted in a few small TV roles on shows such as Peyton Place, Gidget, That Girl, Gunsmoke, Bewitched, The Ghost & Mrs. Muir, and The Big Valley. During the late 1960s and early 1970s, he also performed on stage on Broadway, Off-Broadway, repertory, and improvisational theater.