Prednisone is widely used by most heart transplantation units despite its frequent side effects. Deflazacort, an oral synthetic steroid with fewer side effects, has been successfully used in patients after heart transplantation, but a prospective study comparing deflazacort and prednisone in transplant patients is lacking. We have carried out, in the last year, a prospective trial of deflazacort versus prednisone involving 35 consecutive heart transplant patients. Two of these patients died perioperatively (surgical mortality, 5.7%), and another two were excluded from the protocol because of diabetes mellitus in one patient and active infection before transplantation in the other patient. Thus 31 patients were enrolled in the 3-month study. All of them were treated with antithymocyte globulin, 10 mg/kg/day for 3 days after transplantation, azathioprine, and cyclosporine; patients were randomly assigned groups: 15 patients to receive deflazacort therapy, 1.5 mg/kg/day, and 16 patients to receive prednisone therapy, 1 mg/kg/day, starting the first day after transplantation. Steroids were rapidly tapered, reaching the maintenance dose at 2 to 3 weeks after transplantation (prednisone, 0.15 mg/kg/day; deflazacort, 0.25 mg/kg/day). Both groups were similar in terms of age, gender, ABO identity, serum cyclosporine levels, azathioprine dosage, and pretransplantation serum glucose and lipids levels. Seven endomyocardial biopsies were performed on each patient, at 1, 2, 3, 5, 7, 10, and 13 weeks after transplantation. Incidence of acute rejection was similar between prednisone and deflazacort groups; 33% of patients receiving prednisone therapy and 42% of patients receiving deflazacort therapy had one episode of 3A or higher rejection (not significant).(ABSTRACT TRUNCATED AT 250 WORDS)