This study was designed to evaluate the effects of propofol on mean arterial pressure (MAP) and systemic vascular resistance (SVR) during cardiopulmonary bypass (CPB). Twenty patients were divided randomly for administration of 2 mg.kg-1 propofol (group Propofol, n = 10) or 0.9% saline solution (group Control, n = 10) during CPB. The two groups were comparable with respect to sex, age, height, type of surgery (valvular or coronary), arterial hypertension and preoperative antihypertensive treatment. Only their weight and body surface area were significantly different (control group vs propofol group, respectively: 78.5 +/- 14.4 vs 64.7 +/- 7.7 kg, P < 0.05; and 1.85 +/- 0.2 vs 1.68 +/- 0.13 m2, P < 0.05). MAP, SVR and SVR index were significantly lower in the propofol group than in the control group at 10, 15 and 20 min of study, suggesting that the hypotensive effect of a bolus injection of propofol is due, at least in part, to a direct decrease in the SVR.