Cadmium exposure results in a time and dose-dependent reduction in sperm count. The control and each cadmium-exposure group (5 mg/L, 50 mg/L, and 100 mg/L) were composed of five Wistar rats. Sperm count was determined individually for the left and right cauda epididymes of each rat and then totaled. Sperm counts (in term of millions of sperm) are presented as means with standard errors. An inverse relationship between cadmium dose and sperm concentration was detected after 4 wks of exposure (ANOVA, P < 0.018). Post hoc pairwise comparisons indicated that sperm counts of control animals and those exposed to 5 mg/L cadmium were indistinguishable (H-S, P = 0.252, not significant). At exposures of 50 mg/L and 100 mg/L, however, there was a dose-dependent decrease in sperm counts as compared with controls (H-S, respectively, P < 0.028 and P < 0.003).