Infectious complications developed postoperatively in 12 of 20 patients undergoing cardiac transplantation. In five, infection was considered to have caused or contributed directly to death. In the remaining 7 patients 20 separate infectious episodes were arrested or cured. A wide variety of infectious organisms were seen, including bacteria, fungi, viruses, and protozoa. Multiple infections, especially pulmonary, were common, and many were recognized only at autopsy. Although immunosuppressive treatment was considered the primary factor in predisposing to posttransplant infection, other factors, including the respiratory complications of chronic congestive heart failure and surgical management in the cardiac recipient, were considered contributory. This experience demonstrates that in cardiac transplantation, as in other types of organ transplantation, infectious complications constitute a major cause of postoperative morbidity and mortality.