The combined effect of continuous blockade of glucagon and cortisol by somatostatin and etomidate and thoracic epidural analgesia on hepatic conversion of amino nitrogen was studied in eight patients who underwent elective cholecystectomy on day 1 after operation and was compared with 16 patients who underwent operation without blockade. Surgery increased the plasma clearance of total alpha-amino nitrogen from 5.2 +/- 0.3 to 6.6 +/- 0.3 ml/sec (mean +/- sem; p less than 0.05). This increase was due to increased elimination by the liver, because the hepatic effectiveness for amino nitrogen conversion measured by the functional hepatic nitrogen clearance increased from 9 +/- 2 to 16 +/- 4 ml/sec (p less than 0.05). In contrast, during the combined neural and hormonal blockade, surgery decreased the plasma clearance of amino nitrogen from 5.3 +/- 0.3 to 3.9 +/- 0.3 ml/sec (p less than 0.05), and the blockade prevented the postoperative increase in functional hepatic nitrogen clearance. The results suggest that glucagon, cortisol, and afferent neural reflexes are mediators of the hepatic contribution to catabolism after operation.