The infectious complications during different time intervals after allogeneic bone marrow transplantation (BMT) (day 0 to day 30, 31 to 100, 101 to 365, 366 to 730) were reviewed in 67 adult patients, 27 of whom received transplants without T-cell depletion (TCD) using methotrexate or cyclosporin A for prophylaxis of graft-versus-host disease (GvHD) and 40 of whom received donor marrow with TCD using the monoclonal anti-lymphocyte antibody campath-1 and human complement. The use of TCD reduced the incidence and severity of GvHD significantly (p less than 0.01), but was associated with an increased rate of graft rejections. During all time intervals patients with TCD had a similar, lower or statistically significantly lower number of bacterial, fungal or viral infections and a statistically significantly lower number of lethal infections (p = 0.05) as compared with patients without TCD. This finding might be explained by the fact that with TCD immunological reconstitution can take place unimpaired by GvHD or its prophylaxis or treatment, resulting in a decreased incidence of infections.