The role of steroids in heart surgery was assessed in a group of 95 patients undergoing cardiopulmonary bypass. The treated group (47 patients) received repeated doses (every six hours) of methylprednisolone (30 mg/kg IV) in a double-blind, randomized fashion. The control group (48 patients) received a placebo in a fashion identical to the treated group. There were no significant (P less than 0.1) hemodynamic or biochemical differences between the control group and the patients receiving methylprednisolone. An improvement in survival was observed in the group receiving methylprednisolone. This finding cannot be explained with the data obtained from this study, in particular, when no other biochemical findings were improved. A more exhaustive hemodynamic and biochemical analysis is necessary to understand the subtle changes that are incurred with the use of steroids for heart surgery.