We have studied, in 150 patients undergoing elective general surgery, the effect on gastric content of omeprazole 40 mg, ranitidine 300 mg and famotidine 40 mg, given orally the night and the morning before surgery. Volume and pH of gastric content were measured at induction and recovery from anaesthesia. Gastric volumes did not differ between groups. The median gastric pH was lower with omeprazole compared with ranitidine and famotidine at intubation (5.11, 7.05 and 6.99, respectively) (P < 0.001) and extubation (6.41, 6.98 and 6.96) (P < 0.001). The proportion of patients with gastric pH < 2.5 at induction was 40% for omeprazole, 12% for famotidine and 10% for ranitidine (P < 0.02); the proportion did not differ significantly at extubation.