The effect of ranitidine, the H2-receptor antagonist, on the systemic bioavailability of ethanol (0.3 g/kg body weight) taken orally 1 h after breakfast, was investigated in a randomized, placebo-controlled, double-blind cross-over study. Twenty normal male subjects (age, 19-26 yr) were studied on the morning of the 8th day of twice-daily dosing with either 150 mg ranitidine or placebo. Plasma ethanol concentration was measured by the alcohol dehydrogenase method from 0 to 240 min after oral ingestion of ethanol (100% ethanol made up to 200 ml orange juice). Compared with placebo, dosing with ranitidine resulted in nonsignificant changes in either the mean integrated 4-h plasma ethanol concentration (27.8 vs. 32.4 mg.h/dl), the peak plasma ethanol concentration (18.0 vs. 21.1 mg/dl), or the time to peak (43 vs. 40 min). There is no clinically important interaction between ranitidine and a low dose of ethanol taken orally 1 h after breakfast.