The systemic cytokine response to major surgical trauma was studied in 20 patients undergoing elective aortic surgery and five patients after inguinal hernia repair. Tumour necrosis factor alpha and interferon gamma were not detected in these patients. An early and short-lived interleukin 1 beta (IL-1 beta) response to major surgery was detected only by intensive sampling in the perioperative period. The IL-1 beta peak preceded a more marked interleukin 6 (IL-6) response that peaked 4-48 h after surgery. IL-6 levels had fallen sharply by 48-72 h in all patients who had an uneventful postoperative course. The IL-6 peaks were significantly lower after hernia surgery than after major aortic operations (P < 0.001); IL-1 beta was not detected in any samples. Three patients undergoing aortic surgery developed unexpected major postoperative complications. IL-6 levels in this group were significantly higher than those of the other patients undergoing aortic surgery within 6-8 h of skin incision, and remained elevated for longer. These rises in plasma IL-6 levels preceded the clinical onset of major complications by 12-48 h. The systemic IL-1 beta and IL-6 response to surgical trauma increased with the severity of the surgical insult. An early, exaggerated IL-6 response was associated with the subsequent clinical development of major complications.