Twelve stable cirrhotic patients with ascites received a 20 mL/kg water load. Seven patients had abnormal water excretion (27.3% +/- 5.4% of the water load in 5 hours) and a minimal urine osmolality of 262 mosmol/kg water. Five patients excreted 82.6% in 5 hours and had a minimal urine osmolality of 65 mosmol/kg water. Mean plasma arginine vasopressin values after water load were significantly higher in Group 1 (1.34 +/- 0.36 pg/mL) than in Group 2 (undetectable). An effective blood volume lower in Group 1 than Group 2 patients was suggested by a lower plasma albumin (2.5 versus 3.3 g/dL, p less than 0.02), a higher pulse rate (96 versus 72, p less than 0.001), a higher plasma renin activity (7.8 versus 1.5 ng/mL . h, p less than 0.005), a higher plasma aldosterone (66 versus 21 ng/dL, p less than 0.05), and a lower urinary sodium excretion (2.7 versus 14.2 meq Na/5 h, p less than 0.005). The results suggest that nonosmotic stimulation of vasopressin secondary to a decrease in effective blood volume is an important factor in the abnormal water excretion of cirrhosis.