Low doses of 95% ethanol (.03 ml/kg/min), infused intravenously into chronically instrumented lambs, rapidly caused severe pulmonary vasoconstriction and moderate systemic vasoconstriction at low blood alcohol levels. The effect of ethanol was dose dependent. Pulmonary vascular effects of 70% ethanol, but not of 95% ethanol were ameliorated by 100% oxygen. From these data, we speculate that ethanol may have a competitive interaction with the cellular mechanism(s) that transduce oxygen induced pulmonary vasodilation.