A renal transplant involving a recipient with a positive serological cross-match against donor lymphocytes generally results in hyperacute rejection of the graft. 13 cadaveric renal transplants were performed in recipients with a known positive serological cross-match against donor B lymphocytes. 12 of these serological cross-matches were positive against donor blood, node, or spleen lymphocytes, but the reactivity was directed against donor B lymphocytes only. 3 transplants failed, 2 because of rejection and 1 because of renal-artery thrombosis. 10 transplants are functioning, 6 to 42 weeks after the operation. Of these 10 successful grafts, 3 had no acute rejection episodes, while 7 had an early acute rejection episode which responded to treatment. Histologically, the grafts showed a cellular rejection, similar to that in enhanced renal allografts in the rat. It is possible to transplant a kidney in a high-risk patient with a positive B lymphocyte cross-match with a low risk of failure. In addition active enhancement of the graft might sometimes occur.