Pretransplant sera of 474 kidney graft recipients were tested for IgG-anti-F(ab')2 gamma activity. The patients had significantly higher IgG-anti-F(ab')2 gamma activity than healthy controls (P = 0.0004). Serum lymphocytotoxic antibodies were correlated with IgG-anti-F(ab')2 gamma (P = 0.004), whereas CMV infection and blood transfusions were not. We found a significant association between pretransplant IgG-anti-F(ab')2 gamma activity and early and 1-year kidney graft outcome. This association was pronounced in recipients with no lymphocytotoxic antibodies. Recipients with immediately functioning grafts and a creatinine < 130 mumol/L at 1 year had strikingly higher pretransplant IgG-anti-F(ab')2 gamma activity than patients with graft failure (P < 0.0001).