Multiple measurements (n = 212) of lymphocyte subsets in 67 children treated with steroid-free Tacrolimus, and rabbit anti-human thymocyte globulin induction demonstrate early reconstitution of T-cytotoxic and NK cells. Reconstitution of CD4+ cells is complete after the second post-transplant year. During the period at risk for rejection, NK and T-cytotoxic cell counts are significantly higher among Rejectors. During periods at increased risk for EBV viral infection, CD4 counts bear a significant inverse relationship to EBV viral load in a subset of at-risk recipients. Rejection-prone children also demonstrate significantly higher counts of total lymphocytes, Tc and NK cells prior to SBTx, and may illustrate one basis for enhanced baseline immunocompetence.