During the first year after orthotopic heart transplantation 39 recipients (given prophylactic immunosuppression with antithymocyte globulin for 7 days after orthotopic heart transplantation and triple drug maintenance therapy) were screened for cytomegalovirus antigenemia and anti-cytomegalovirus immunoglobulin M (index) and immunoglobulin G levels (antibody units) by MEIA-method. Until day 14, all recipients received cytomegalovirus hyperimmunoglobulin at a dosage of 2 ml/kg/day. Four patient groups were defined: group 1 (n = 15) seropositive recipient/seropositive donor, group 2 (n = 9) seronegative recipient/seropositive donor, group 3 (n = 8) seropositive recipient/seronegative donor and group 4 (n = 7) seronegative recipient/seronegative donor. Twenty-four donors and 23 recipients were seropositive for anti-cytomegalovirus immunoglobulin G. After transplantation, 31 recipients tested positive for cytomegalovirus antigenemia before immunoglobulin M elevation and at least 7 days before the onset of clinical symptoms of cytomegalovirus. In group 2, episodes of cytomegalovirus antigenemia appeared earlier, were more frequent, and lasted longer than in groups 1 and 3. Without previous evidence of positive cytomegalovirus antigenemia testing, no sign of cytomegalovirus disease was seen. When cytomegalovirus antigenemia was positive, cytomegalovirus hyperimmunoglobulin was readministered at the same dosage and gancyclovir (1000 mg/day) was given until cytomegalovirus antigenemia disappeared. However, episodes of recurrent cytomegalovirus were observed (2.6 +/- 1.9, 4.3 +/- 1.0, and 2.3 +/- 1.2 in groups 1, 2 and 3, respectively). In groups 1 and 3, the anti-cytomegalovirus immunoglobulin G antibody level remained high during the observation period. In groups 2 and 4 anti-cytomegalovirus immunoglobulin G antibodies were positive because of hyperimmunoglobulin prophylaxis but immunoglobulin G decreased again after discontinuation of the prophylaxis.(ABSTRACT TRUNCATED AT 250 WORDS)