In a double-blind study, 107 patients undergoing elective and emergency surgical procedures were given 15 ml of either sodium citrate 0.3 M or placebo 10 minutes before induction of anaesthesia. Gastric contents were sampled immediately after induction and the pH was measured. The mean pH of the Gastric contents of patients given sodium citrate was 5.67, whereas for those given the placebo it was 3.21 (p less than 0.001). Of patients given sodium citrate 92% had a gastric pH above 3.0 compared with only 37% in the placebo group (p less than 0.001). At the end of surgery gastric contents were emptied as completely as possible and the volume and pH measured. There was no significant difference in the mean volume of gastric contents in the two groups. In neither group was the mean pH at the end of surgery significantly different from that after induction.