Histamine 2 (H2) receptor antagonists are clinically very useful drugs for the treatment of peptic ulcers. We undertook this study to investigate the effects of therapeutic and double therapeutic dose levels of H2 antagonists, cimetidine and ranitidine, on reproductive parameters and serum levels of hepatic enzymes in the Wistar rat. Cimetidine (30 or 60mg/kg/day), ranitidine (8 or 16mg/kg/day) and vehicle (1ml/kg/day) were administered to different animal groups (n=8) by gastric gavage for 14days. Animals were sacrificed and blood serum levels of alkaline phosphatase (ALP), aspartate transaminase (AST), and alanine transaminase (ALT) were measured. Epidydimal sperm and histological analyses of the testis were also performed using standard methods. Cimetidine and ranitidine had no significant (p>0.05) effects on ALP, AST and ALT levels. Ranitidine had no significant effect on all sperm and histological parameters evaluated. Cimetidine causedsignificant (p<0.05) and dose-dependent decreases in sperm count and motility, without an effect on sperm morphology and viability. Cimetidine also caused alterations in the histology of the testis. We conclude that subchronic administration of clinical dose levels of cimetidine may alter testicular function, possibly via direct adverse effects on the seminiferous tubules, while ranitidine may not. Cimetidine and ranitidine may not impair normal hepatic biochemical function.