Although an impairment in renal water excretion is a commonly encountered clinical problem in cirrhotic patients, the mechanisms responsible for this abnormality are uncertain. ADH levels are elevated in some patients with decompensated cirrhosis, but a causal relationship between these levels and impaired water excretion has not been established. Since in normal man, water immersion to the neck (NI) results in a preferential central hypervolemia (CV), without plasma compositional change, and a resultant suppression of AVP, we designed the present study to determine if the diuretic response of cirrhotic patients to NI is mediated by a decrease in AVP. 17 cirrhotic patients with ascites were studied following 14 h of dehydration on two occasions: during a seated control study (C) and during 4 h of NI. AVP, determined by RIA, was measured every 30 min. 12 of the 17 patients manifested a diuresis that equalled or exceeded that documented in normal hydropenic subjects during immersion. NI did not alter mean AVP as compared with either the pre-study hour or those of the corresponding control study. Furthermore, peak V and CH2O varied independently of prestudy AVP (r = -0.116), mean change in AVP (r = -0.060), as well as nadir AVP levels (r = -0.122). The demonstration of a diuresis in some of the subjects, occurring without concomitant suppression of plasma AVP, suggests that ADH may constitute a permissive rather than pivotal factor in the impaired water excretion of many patients with advanced liver disease.