To explore the mechanism responsible for puromycin aminonucleoside induced-nephrotoxicity, metal content was preliminarily investigated in the kidneys of rats that had received a single subcutaneous injection of the agent (80 mg/kg body weight). In the group that received this agent, the renal content of Fe rose on days 5, 10, and 15; that of Cu fell on days 10 and 15; that of Zn rose on day 5; that of Se fell on day 10; there were no changes in Mn throughout the experimental period. Providing that these findings directly involved the renal activities of superoxide dismutases and glutathione peroxidase, the renal reduction of Cu and Se gave proof counter to previous findings of an enzymatic protective system against possible attacks by the oxygen radicals.