The effects of acute ethanol intake (1.5 g/kg) on plasma testosterone and luteinizing hormone (LH) concentrations were examined in male Long-Evans rats. Ethanol decreased the serum LH concentrations by 21% and 42% 30 and 60 minutes after ethanol administration respectively. The testosterone concentrations decreased later (30 min: +8%; 60 min: -30%). The LH concentrations were highly correlated with subsequent (60 min later) testosterone concentrations (LH30min: r = .688, p less than 0.001, n = 25; LH60min: r = .678, p less than 0.001), but less so with concurrent testosterone concentrations (30 min: r = .187, N.S.; 60 min: r = .552, p less than 0.004). To further test the influence of LH, naloxone (11 mg/kg) was administered, which elevated the LH levels within 30 min by 103% in controls. Naloxone also increased serum LH concentration by 34% in ethanol-treated rats at 30 min, but these animals nevertheless had lower (p less than 0.01) testosterone levels at 60 min than did control animals without naloxone and ethanol treatment. It is concluded that although ethanol-induced changes in serum LH levels may play a role in the decrease of serum testosterone concentrations in rats, there are also other mechanisms by which ethanol may produce these effects.