Abstract: It is well documented that small dose of prostaglandins is stimulatory to spermatogenesis, but as to the effect of large dose, the views were contradictory. The present study was oriented primarily toward clarifying this Problem. Eighteen adult male rats were divided at random into 2 groups (treated and control) of 9 rats each. To the treated rats, PGE (E₁:E₂=1:1) was given subcutaneously in a daily dose of 3.0 mg/kg for 22 days. On the 23 rd day, the animals were sacrificed and tissue samples taken for different observations. Conspicuous damage of early spermatids and pachytene spermatocytes, and occasionally spermatogonia was found in the treated group with marked decrease in motility and increase in malformed ones of the spermatozoa of cauda epididymides. In the treated group, the PGE level in testis was significantly increased but not in renal cortex and blood plasma. The significance of these findings were discussed.