The dose-response for glycopyrrolate and heart rate in anesthetized children has not heen defined. We determined the dose-response for glyeopyrrolate and heart rate in 50 children, ASA physical status l and 2, anesthetized with halothane and nitrous oxide. Anesthesia was induced with 60-70% nitrous oxide in oxygen and halothane(1.5-2.0 vo1%). After induction of aneethesia, glycopyrrolate in a dose of 4, 6, 8, 12 or 16ug Xkg(-1) was administered by rapid infusion to each subject. The effects of glycopyrrolate on heart rate, heart rhythm and systolic blood pressure were compared among dosage groups, and dose-response curve for peak heart rate was constructed, Glycopyrrolate increased the heart rate in a dose-related manner upto 12 ug X kg(-1) except 16 ugX kg(-1). Fifty percent maximal response corresponded to 6.1 ug X kg(-1), and 95% maximal response corresponded to 11.1 ug X kg(-1) . None of the patients had nonsinus rhythm after glycopyrrolate injection. Except for glycopyrrolate given at 4 ug x kg(-1), the systolic blood pressure increased significantly after all other doses. Glycopyrrolate in doses greater than or equal to 6 ug X kg(-1) increased the heart rate and systolic blood pressure in children anesthetized with halothane and nitrous oxide.