Plasma levels of alpha-human atrial natriuretic peptide (alpha-hANP), renin activity and angiotensin II were studied in 17 patients undergoing partial hepatectomy. Central venous pressure (CVP), heart rate (HR), mean arterial pressure (MAP) and the serum sodium concentration (Na), which affect plasma ANP levels, were measured during the operation. At 90 minutes after the surgical incision, plasma alpha-hANP levels increased significantly from 38.6 +/- 4.02 pg.ml-1 to 62.7 +/- 8.24 pg.ml-1, but the changes in plasma alpha-hANP levels during the surgery were within normal levels. Plasma alpha-hANP levels were not related to changes in CVP, HR and Na. At 90 minutes after the incision when plasma alpha-hANP levels were elevated, plasma renin activity, angiotensin II and MAP also increased significantly. Therefore, we believe that activation of the sympathetic nervous system by surgical stimulation is one of the causes of the elevation of alpha-hANP levels during the operation. The increase in plasma alpha-hANP levels, however, was lower than those of the plasma renin activity and angiotensin II. Our results suggest that surgical stimulation acts to retain sodium and water in patients during partial hepatectomy.