This study evaluated the clinical significance of interleukin-6 levels after hepatectomy. Thirty-one patients who underwent hepatectomies were examined. Perioperative data involving serum laboratory tests, serum concentrations of interleukin-6, and liver energy status as indicated by arterial ketone body ratio (AKBR) were analyzed. In each patient, the maximum concentration of interleukin-6 in the postoperative course (IL-6-M) was observed by the 2nd postoperative day. IL-6-M correlated significantly with the maximum concentration of total bilirubin and with the postoperative decrease in AKBR. IL-6-M also correlated with the duration of surgery and blood loss, but no relationship with aminotransferase was found. We conclude that after hepatectomy IL-6-M may be a marker for the metabolic status of the liver as well as operative stress, and is useful because it can be evaluated in the early postoperative period.