Since infections with Herpetoviridae after kidney transplantation still remain a major clinical problem, we conducted a double-blind, placebo-controlled trial using low-dose recombinant interferon-alpha-2C (rIFNa2C) prophylaxis in 50 renal graft recipients immunosuppressed with cyclosporine and methylprednisolone. Ten patients were excluded from further analysis because of graft loss due to surgical complications, side effects of rIFNa2C, and because of lack of compliance. There was a significant difference in graft loss due to irreversible rejections between the verum and the placebo group (6 vs. 0; P less than 0.05), whereas no difference was observed with regard to the occurrence of viral infections. We conclude, that low-dose rIFNa2C prophylaxis is harmful in renal allograft recipients treated with cyclosporine in view of the high incidence of irreversible transplant rejections without beneficial effects on the occurrence of viral infections.