Survivors of allogeneic marrow transplants are immunodeficient for at least 1 year after grafting. Multiple defects of immunity have been found; however, it is not known which defect primarily accounts for the high infectious morbidity of these patients. Twenty‐nine allograft recipients who were in complete remission of the original disease were examined for the following parameters of immunity at 1 year after transplant: infection score (gauging the number and severity of infections within the 6 months prior to the annual exam), serum total IgM, IgG, and IgA, anti‐Haemophilus influenzae IgG, anti‐Streptococcus pneumoniae IgG, skin test reactivity, and the blood counts of B cells, CD4⁺ T cells, CD8⁺ T cells, and their subsets. THe only parameter inversely correlated with the infection score was CD4⁺ T cell count (P = 0.005 in univariable analysis, P = 0.06 in multivariable analysis). We conclude that infectious morbidity of long‐term transplant survivors is related to the reconstitution of CD4⁺ T cells. Am. J. Hematology 54:131–138, 1997 © 1997 Wiley‐Liss, Inc.