Lymphocytotoxic antibodies against peripheral blood lymphocytes (LT anti-PBL) were investigated in sera obtained before and after 148 kidney transplantations. Reactivity was assayed on a panel of unrelated donor cells and, in 15 cases, on the kidney donor's lymphocytes. Pretransplant LT anti-PBL, whether they persisted or not after grafting, were of no prognostic value. However, they were associated with longer periods of treatment by chronic hemodialysis, due to an increased frequency of positive cross-matches against potential donors. De novo occurrence of LT anti-PBL after transplantation was more frequently observed in mismatched kidney recipients, and they were significantly correlated to graft failure. In this respect, LT specifically directed to the kidney donor are of more avail than those directed to the panel. Anti-B lymphocyte LT do not seem to be more specific or more predictive for the follow-up of these patients.