We have assessed the efficacy of a single dose of lansoprazole in increasing the pH and decreasing the volume of gastric residue at induction of anaesthesia in adult patients undergoing elective orthopaedic surgery. We studied 66 ASAI-II patients, allocated to one of three groups to receive either placebo (group 1), lansoprazole 30 mg (group 2) or lansoprazole 60 mg (group 3), 8-12 h before induction of anaesthesia. Volume and pH of gastric contents were measured after induction of anaesthesia by aspiration via a 16-French gauge gastric tube. Patients who received lansoprazole had a significantly higher pH than the placebo group (P < 0.01) but there was no difference between the two lansoprazole groups. The volume of gastric residue was significantly smaller (P < 0.01) in both lansoprazole groups compared with the placebo group: 28% of those in group 3 had a pH of gastric residue < 2.5 and volume > 25 ml compared with 30% in group 2 and 63% in group 1, respectively.