Anti-B cell, anti-T cell, and antiperipheral blood lymphocyte antibodies were investigated in the sera from 115 cadaveric kidney graft recipients pre- and post-transplantation. These antibodies were characterized: optimal temperature for cytotoxicity (4 C or 22 C), immunoglobulin class (IgG or IgM), and reactivity after platelet absorption, and thereafter defined according to their influence on the graft survival. Patients with IgM anti-B cell antibodies, reacting mostly at 4 C, the activity of which could not be removed by platelet absorption, have a prognosis of the graft as good as those with no antibody, i.e., the graft function (serum creatinine and severity of rejection) at 3 years was comparable between those two groups. However, when the anti-B cell antibodies unabsorbable on platelets are of IgG class and detected at 4 C and 22 C, the graft outcome is poorer (P less than 0.025 at 3 months). A similar prognosis is observed in patients with antiperipheral blood lymphocyte antibodies of IgG or IgM class, absorbable or not on platelets (P less than 0.05). Lymphocytotoxic antibodies of the IgG class are always associated with a poor graft outcome. On another hand, the cold anti-B cell antibodies of the IgM class are not associated with graft failure but no enhancing effect could be seen.