Blood ethanol concentrations after separate oral dosing and intravenous infusion of ethanol (0.15 g/kg) were measured in 16 control subjects and 13 subjects treated with ranitidine. All subjects underwent routine upper gastrointestinal endoscopy. Peak blood ethanol concentrations, and area under the blood ethanol/time curve, were significantly higher in the ranitidine group after oral, but not intravenous, ethanol administration. The first pass metabolism, as calculated by the difference between the area under the curves, was significantly lower in the ranitidine group. In addition, all subjects withdrawn from ranitidine (n = 6) had a significant reduction in peak blood ethanol concentration and area under the curve after repeat dosing with oral ethanol. Both groups were well matched for age, sex, indications for endoscopy, findings at endoscopy, and gastric histology. These findings show that ranitidine increases the bioavailability of low dose ethanol and has possible short term forensic, and longterm physical implications for moderate drinkers who are taking the drug.