The influence of continuous immunosuppression on the immune system of 2 neonates born to heart-lung transplant recipients was analyzed. T cells, T cell sub-populations, B cells and cyclosporine levels were measured in maternal and cord blood at the time of delivery. Cyclosporine, both parent compound, and metabolites were found in cord blood but in lower amounts than that in the mother. This discrepancy was more pronounced for parent compound than metabolites. Infants born to immunosuppressed mothers had more T and B cells than the mother and had similar numbers of T and B cells to that found in cord blood from 10 babies born to nonimmunosuppressed mothers. One infant had fewer activated T cells and a higher CD4/CD8 ratio due to increased numbers of CD4 cells than normal. In conclusion, neither of these babies had a lymphocyte profile suggestive of chronic immunosuppression.