Big John, Little John was a sit-com that aired in 1976 on NBC.

The show centered around a forty-year-old middle school science teacher named John Martin (played by Edelman). While vacationing in Florida, he drinks from a spring which turns out to be the legendary Fountain of Youth sought by Juan Ponce de León. The water changes him into a twelve-year-old boy (played by Rist), and back again.