To compare the effects of atracurium, 0.75 mg/kg, on the mean arterial pressures, heart rates and plasma histamine levels under 2%-enflurane inhalation with mask, 24 patients were allocated randomly into two groups; one(Group I, n=12) which atracurium was administered with rapid bolus injection for 5 seconds and the other(Group II, n=12) with the slow injection for 75 seconds. In both groups, there are the most significant decreases and the recovery in mean arterial pressure 1~2 min and 5 min after atracurium, respectively, Group I showed a significant decrease of mean arterial pressure about 10% more than Group II. In heart rate, there are the significant decreases gradually to 87~88% of control 5 min after atracurium in both graups except the only significant increase(104%) 1 min after atracurium in Group I. And Group I showed a significant increase(200%) in plasma histamine concentration (p< 0.05) 2 min after injection than before, but Group II did no significant change. In conclusion, the slow injection of atracurium over 75s during induction of anesthesia can attenuate the histamine-induced cardiovascular response.