To test whether a pulse of testosterone reported in young male garter snakes also occurs in related snakes, testosterone levels were measured in 18 male water snakes (Nerodia sipedon) belonging to four litters at 5–6, 16–17, 29–30, and 250–267 days of age. Testosterone levels were uniformly low over the first 30 days of life but increased significantly by 250–267 days of age; there were also significant differences among litters in levels of this hormone by that time.