Ninety patients presented for elective surgery and were randomly divided into three groups and studied on a double-blind basis to assess the efficacy of gastrozepin, a new muscarinic receptor antagonist, compared to cimetidine and placebo. Gastrozepin 10 mg, cimetidine 200 mg and a placebo were given i.v. on average 90 min prior to surgery. Gastric fluid was aspirated immediately after induction of anaesthesia and the volume and pH measured. The mean gastric fluid volume in the placebo group (19.73 ml) was significantly (P less than 0.02) greater than the mean volume of either the gastrozepin group (12.40 ml) or cimetidine group (12.72 ml). Mean gastric pH's were 4.83 (gastrozepin), 6.39 (cimetidine) and 3.21 (placebo) and each of these means differed significantly from the other two (P less than 0.001). However, the number of patients who had a gastric juice volume of more than 25 ml and a pH of less than 2.5 in each of the three groups: gastrozepin, cimetidine and placebo, were 1, 0, and 8, respectively.