Cadmium in water given ad libitum reduces sperm motility. Sperm motility was determined individually for the left and right cauda epididymes of each rat in the control group (n = 5) and the cadmium-exposed groups (5 mg/L, n = 5; 50 mg/L, n = 5; and 100 mg/L, n = 5). Data are presented as sperm motility of cadmium-treated rats as a percentage of that of control animals. A dose-dependent decrease in sperm motility was observed after exposure to cadmium for 4 wks (ANOVA, P < 0,007; H-S, P < 0,025 to P < 0,001). Sperm motility at 8 wks of cadmium treatment was lower than at 4 wks, and the effect of dose was no longer apparent (ANOVA, P = .239, not significant).