In this study, we have compared the influence of CsA and pred/aza on the immunocompetence in man. Therefore, kidney-transplant recipients were tested for their primary keyhole limpet hemocyanin and secondary (tetanus and KLH) humoral immune responses and their primary dinitrochlorobenzene and secondary (recall antigens) cellular immune responses. We demonstrate that primary immune responses are inhibited by CsA, whereas secondary immune responses are relatively resistant. Pred/aza therapy seems to inhibit all cellular immune responses, as we demonstrated before, as well as the primary humoral immune responses. Secondary humoral immune responses are only slightly affected by pred/aza. Our results provide a strong argument for starting immunosuppression with CsA, either with or without a low-dose pred.