We studied the circulatory and respiratory effects of methylprednisolone (MPS) associated with catecholamine administration of a few hours after cardiopulmonary bypass (CPB). Forty patients undergoing coronary artery bypass grafting were randomly divided into two groups. Twenty patients in group 1 [MPS (-) group] did not receive MPS and 20 patients in group 2 [MPS (+) group] received MPS 15 mg.kg-1 i.v. 60 minutes after CPB. The circulatory and respiratory parameters were measured 60 minutes after CPB, 30 minutes after MPS i.v. and 60 minutes after MPS i.v. The values in MPS (-) group were compared with those in MPS (+) group. CI and SVI decreased, and SVRI and PQR increased in MPS (-) group, but these values were unchanged in MPS (+) group. RAP, mPAP, PCWP and PVRI were unchanged in MPS (-) group. PCWP increased and the other values were unchanged in MPS (+) group. The blood gases and pulmonary alveolar function were not different between the two groups. The oxygen delivery decreased in MPS (-) group, but it was unchanged in MPS (+) group. The oxygen consumption was unchanged in the two groups. Blood cortisol increased and epinephrine and norepinephrine decreased in MPS (+) group. Methylprednisolone had an effect to improve the decreased CI and the increased SVRI, and no respiratory problems were observed in patients for coronary artery bypass grafting with catecholamine administration for a few hours after cardiopulmonary bypass.