The effects of preanesthetic glycopyrrolate and cimetidine on gastric fluid pH and volume were studied in outpatients. One hundred outpatients scheduled for elective surgery were randomly allocated into four groups with 25 patients in each group. Patients in group I were given neither glycopyrrolate nor cimetidine and served as controls. Group II patients received 4-5 micrograms/kg of glycopyrrolate intramuscularly 45-90 min before induction of anesthesia. Patients in group III received 300 mg of cimetidine orally with a sip of water 1-4 hr before induction of anesthesia. Group IV patients received cimetidine, as in group III, and glycopyrrolate as in group II. Twenty-five inpatients undergoing elective surgery also were studied for comparison. Patients in group I (control) served as the basis for comparison with inpatients. Patients with gastric pH less than or equal to 2.5 or volume of gastric contents greater than or equal to 20 ml were defined to be at risk of pulmonary damage in the event of aspiration. Patients in group I had a mean gastric pH of 2.34 +/- 0.30 with a mean gastric volume of 25.6 +/- 4.1 ml. Seventy-six % of the patients in the control group had gastric contents with a pH less than or equal to 2.5 and 52% had volumes greater than or equal to 20 ml. Glycopyrrolate (group II) failed to increase gastric pH or to reduce gastric volume. In contrast, cimetidine in groups III and IV with or without glycopyrrolate significantly reduced the number of patients at risk of aspiration, by increasing the pH and reducing the volume of gastric contents.(ABSTRACT TRUNCATED AT 250 WORDS)