The purpose of this study was to measure plasma histamine concentration following the intravenous bolus injection of atracurium in surgical patients and to clarify any correlation of resultant cardiovascular change with plasma histamine release. Twelve elective surgical patients of ASA-I were studied after the approved informed consent. Twenty of blood samples were collected for the assay of plasma histamine at 1 minute before as the control and 1, 3, 5, and 10 minutes after the administration of atracurium 0.6mg.kg-1 or 1.2mg.kg-1 intravenously. Plasma histamine was measured by utilization of the modified single isotope radioenzymatic assay. Blood pressure, heart rate, EKG and cutaneous signs were observed continuously during the study. Intravenous bolus administration of 0.6mg.kg-1 and 1.2mg.kg-1 atracurium which is larger than 2 times of ED95 demonstrated significant changes in heart rate, blood pressure and histamine release. A significant increase in plasma histamine, a decrease in blood pressure and an increase in heart rate occurred at 1 to 3 minutes after the injection of atracurium. Plasma histamine release and cardiovascular changes had strong correlation with the intravenous dose of atracurium.