A clinical trial was undertaken to study endotoxemia in 14 patients with obstructive jaundice given the antiendotoxin polymyxin B, 13 patients with obstructive jaundice who were not given the antiendotoxin , and 13 nonjaundiced control patients undergoing comparable surgery. Endotoxins were detected by the limulus assay. Endotoxemia did not occur in the nonjaundiced patients but was common before (68 percent), during (70 percent), and after (81 percent) surgery in the jaundice patients. Thirty-six percent of the jaundiced patients had postoperative oliguria. Endotoxemia before surgery was associated with death after surgery, all deaths occurring in patients who were endotoxemic before operation (p less than 0.05). Polymyxin B infusion had no effect on endotoxemia or outcome. Measurement of indicators of fibrinolysis, soluble fibrin, and fibrin degradation products showed no prognostic significance. We conclude that preoperative endotoxemia is an important predictor of outcome in patients who undergo surgery for jaundice.