The aim of this study was to examine whether liver transplantation reverses the abnormal distribution of lymphocyte subsets previously observed in biliary atresia children, namely a selective decrease in the naive CD4/CD45RA+ T cell subset and an increase in the B and natural killer cell subpopulations. Eight biliary atresia children aged 1.08 to 6 years were studied before and 1 year after LTx for comparison with 15 age-matched healthy controls. The posttransplant immunosuppressive regimens included prednisone [0.1 mg/kg] and tacrolimus (level range: a 10-12 microg/dL). The percentage, absolute cell number, and receptor density were assessed by the use of double color flow cytometry (EPICS-XL MCL fluorocytometer). Biliary atresia patients were compared after LTx with subjects before LTx, essentially showing no statistically significant changes in lymphocyte subsets. We conclude that LTx of biliary atresia children does not reverse the abnormal lymphocyte subset distribution present before transplantation. Hence, these changes may reflect either their independence from the liver status or may result from immunosuppressive treatment that contributes to defective CD4+ T cell regeneration reflected by a deficiency in CD4/CD45RA+ naive T cells.