Arterial ketone body ratio (KBR), which reflects the NAD+/NADH ratio of hepatic mitochondria, was measured sequentially in 39 liver transplantations. In 22 cases, KBR was increased to above 0.7 within 6 hr after reperfusion (group A). In 11 cases, restoration of KBR was delayed until the first postoperative day (group B) and in 6 cases, KBR failed to recover (group C). The patients in group A survived liver transplantation without complications. By contrast, morbidity and mortality were significantly higher in groups B and C. In 2 cases in group C, the livers were clinically diagnosed as initially nonfunctioning grafts and the patients underwent retransplantation. Another two died of hepatic failure soon after the operation. It is suggested that delayed recovery of KBR is an early indicator of metabolic overload in the liver allograft, and that a delay exceeding 24 hr may imply the need for retransplantation.