The incidence of infectious complications was monitored in a group of the first 100 patients undergoing orthotopic heart transplantation at the Institute for Clinical and Experimental Medicine from January 1984 through May 1993. The definition of an infectious complication was a clinically manifest infection requiring treatment. Cytomegalovirus infection and Epstein-Barr virus infection were evaluated by the development of antibody against IgM. A total of 168 infectious complications were detected in 80 patients. The infectious complications were fatal in 11 patients; hence, infections were implicated in 26% of all deaths following heart transplantation. The spectrum of infections markedly varies depending on the interval since the procedure. The most frequent infections within the 30 postoperative days are bacterial (often nosocomial) infections. In the later period (30 days onward), viral infections account for 72% of cases. Of the rarer types of infections, the pulmonary form of aspergillosis was identified in 3 cases, nocardiosis and legionellosis in one case each. Infectious complications were the main cause of deaths in the period of 1 to 4 months post-transplantation, and the spectrum and rate of complications were not different from data reported by other centres.