Infectious complication represents a significant source of morbidity and mortality in heart transplant recipients. To assess humoral immunity markers that can predict the development of infection, 38 consecutive recipients of heart transplants performed at a single center were prospectively studied. Induction therapy included daclizumab. Immunoglobulin (IgG, IgA, IgM) and complement factors (C3, C4, and factor B) were performed by nephelometry in peripheral blood samples obtained before transplantation, and 7 days and 1 month after transplantation. During a mean follow-up of 16.9 months, 13 patients had at least one episode of infection (34.2%). Eight of these were cytomegalovirus (CMV) infections treated with intravenous ganciclovir, 2 were bacterial pneumonia, 1 patient had bacterial septicemia, 1 patient had urinary tract infection, and 1 patient had pulmonary nocardiosis. No significant association was found between infection and age, sex, immunosuppression, CMV serostatus of donor and recipient, or treated rejection episodes. Pre-transplant IgG (below median value=1140 mg/dL; relative risk [RR] 3.69; 95% confidence interval [CI] 1.01-13.54; P=0.04) and post-transplant IgG levels at day 7 (below median value=679 mg/dL; RR 11.21; CI 1.04-89.48; P=0.022) were associated with an increase in the risk for developing infections. Early monitoring of immunoglobulin levels might help to identify the risk for developing infection in heart transplantation.