We conducted a prospective study of 12 patients undergoing kidney transplantation. In these patients, we monitored interleukin-8 (IL-8) in both serum and urine before and after kidney transplantation. Levels of IL-8 were analyzed by a solid-phase double ligand ELISA method. Three patients with an uneventful recovery after transplantation showed IL-8 serum levels below the detection limit, whereas some small amounts were detected in the urine of these patients. IL-8 serum levels markedly increased with acute graft rejection and infection. Increments in serum and urine preceded clinical complications in all patients. Highest levels were observed in bacterial infection and lowest in acute rejection. Although nonspecific, IL-8 can be considered as an indicator molecule of inflammatory processes occurring during kidney transplantation.