Galecki made his acting debut in the 1987 CBS miniseries "Murder Ordained" with JoBeth Williams and future "Roseanne" co-star John Goodman. In 1989, Galecki portrayed Rusty Griswold in "National Lampoon's Christmas Vacation". In 1990, he was cast as Danny Nash, the son of Robert Urich's lead character, on the NBC comedy "American Dreamer"; the following season, he was a regular cast member on the ABC sitcom "Billy", a spin-off from "Head of the Class". He appeared in one episode of "Blossom" in 1991, opposite his future "The Big Bang Theory" co-star Mayim Bialik. He played a young delinquent in "A Family Torn Apart", a 1993 TV movie based on a true story about a serial killer.