Forty-two patients undergoing elective general surgery received either placebo, cimetidine 300 mg, or cimetidine 600 mg orally 1.5-2 h before anaesthesia in a double-blind, randomized study. Another 13 subjects received no oral premedication and served as a control group. When compared to placebo or control patients, both doses of cimetidine significantly (P less than 0.01) decreased the acidity and volume of gastric contents. None of the subjects given cimetidine were in the risk range of acid pulmonary aspiration (pH under 2.5 plus volume over 25 ml), whereas 46% of the control patients and 40% of the patients given placebo (P less than 0.005 vs cimetidine in both groups) were in the risk range.