The present study was performed to determine whether testicular toxicity can be detected of the administration of adriamycin (ADR), an anticancer drug, for 2 weeks. ADR was intravenously administered to Slc:SD male rats at 1 mg/kg once a week for 4 or 2 weeks, and 2 mg/kg once a week for 2 weeks. Suppression of body weight gain was observed in the 1 mg/kg/week (4w) and 2 mg/kg/week (2w) groups. The testes weights in these groups were also lower than those of the control group. On histological examination, a decrease in spermatogonia was observed in the 1 mg/kg/week (4w) and 2 mg/kg/week (2w)groups. No abnormalities were detected in the control and 1 mg/kg/week (2w) groups. Stage analysis of seminiferous tubules was performed for control and 1 mg/kg/week (2w) groups. In the 1 mg/kg/week (2w) group, the numbers of spermatogonia in stages II-III, V and XII-XIII were significantly decreased. The numbers of preleptotene spermatocytes in stage VII and zygotene spermatocytes in XII-XIII were also significantly reduced in the same group. These findings suggest that the testicular toxicity of ADR can be detected after 2 weeks administration at a sufficient high dosage, if simplified morphometrical analysis is used.