The effects of short and long-term ethanol administration on plasma testosterone level were studied in rats with vitamin E deficiency. The animals underwent a vitamin E depletion period of 5 weeks followed by an acute dose of ethanol (1 g/kg body wt i.p.). Two hours after the ethanol dose, the plasma testosterone level had decreased both in a control group (-32%, nonsignificant) and in the vitamin E deficient group (-45%, P less than 0.05) as compared with saline-treated rats. The rats which had received an ethanol dose were then exposed to ethanol in the drinking water (10% w/v) for two weeks, after which the acute ethanol dose was repeated. One hour after this second acute dose of ethanol, the plasma testosterone showed a decrease of 24% (nonsignificant) in the control group and 50% (P less than 0.05) in the vitamin E deficient group compared with saline-treated rats. Two hours after the second acute dose of ethanol, the plasma testosterone level was significantly (P less than 0.05) down both in the control group and in the vitamin E deficient group (-41 and -54%, respectively). Thus, vitamin E deficiency strengthened the effect of acute ethanol treatment on plasma testosterone in rats. Long-term exposure to ethanol appeared to sensitize rats to acute doses of ethanol, as judged by the fall in plasma testosterone levels. The present results are in agreement with previous findings in vitro thus supporting the notion that free radicals arising during ethanol oxidation have an inhibitory effect on testosterone synthesis.