Remifentanil is a new potent opioid analgesic that undergoes rapid esterase metabolism. The purpose of this study was to investigate hemodynamic responses to 2-30 micrograms/kg remifentanil (escalating doses) injected as a bolus over 1 min during general anesthesia. After general anesthesia with endotracheal intubation, placement of a radial artery catheter, and pretreatment with glycopyrrolate, remifentanil 2, 5, 15, or 30 micrograms/kg (six patients, three male and three female per group) was administered over 1 min. Arterial blood pressure and heart rate were measured noninvasively before drug administration, after drug administration, and then every minute for 5 min. Arterial blood was taken for histamine determinations before drug administration and then at 1, 3, and 5 min after drug administration. Administration of remifentanil was associated with a reduction in systolic blood pressure from 134 +/- 18 to 91 +/- 16 mm Hg and heart rate from 99 +/- 20 to 69 +/- 21 bpm and was not associated with alterations in histamine concentration.