The effects of premedication on gastric juice volume and pH were evaluated in five groups of 206 pediatric patients undergoing elective surgical procedures: Group 1 (Control) received no premedication; Croup 2 was given morphine sulfate and pentobarbital as premedicants. The other groups received, in addition to morphine and pentobarbital. atropine (Group 3), scopolamine (Group 4), or glycopyrrolate (Group 5). After endotracheal intubation, gastric aspirates were examined for volume, pH and color. Neither premedication with morphine and pentobarbital nor addition of atropine or scopolamine to the premedication significantly altered volume. In patients treated with glycopyrrotate, volume was reduced to less than a third of that of patients in Group 1 (P> 0.001), and the percentage ofpH's higher than 2.5 was significantly greater than in other group. The incidences of unobtainable sample and samples withpH's higher than 2.5 were greatest with atropine (32.0 per cent,P< 0.05) and glycopyrrolate (58.1 per cent,P< 0.01). In 60 per cent of the bile-stained specimens,pH's were below 2.5. It is concluded that because of its selective inhibitory effect on gastric acid secretions, glycopyrrolate appears superior to other anticholinergic drugs. The reduction of gastric juice volume and acidity produced by glycopyrrolate would have important clinical implications in case of accidental aspiration. It is also concluded that bile staining of gastric contents is not a reliable indicator of gastric juicepH.