During the year February 1983 - February 1984 10 patients received immunosuppressive therapy with cyclosporin A (CYA) and methylprednisolone (MP) after either heterotopic or orthotopic heart transplantation. Two of these patients were undergoing severe acute rejection episodes (intractable to conventional immunosuppressive therapy) when CYA administration was initiated; both episodes were reversed and neither patient suffered further rejection. The remaining 8 patients received CYA from the time of transplantation. Two patients died 7 to 9 days postoperatively from multi-organ failure; in retrospect, excessively high dosages of CYA were administered, resulting in very high blood levels of the drug, which may have contributed to renal failure. One patient died (while living abroad) of a possible septicaemia 8 months after transplantation, having otherwise done well. Seven patients remain alive and active 3 1/2 -15 months after operation. The incidence of both severe acute rejection episodes and life-threatening infection would appear to be lower in patients receiving CYA and MP when compared with earlier patients at our institution who received conventional immunosuppression. Frequent monitoring of whole-blood levels of CYA is necessary to ensure that the nephrotoxic effect of the drug is minimized.