The redistribution of blood volume and concomitant central hypervolemia induced by water immersion to the neck (NI) results in a significant natriuresis, kaliuresis and diuresis. The NI model was utilized to assess the role of effective volume and hyperaldosteronism in the impairment of Na and water handling in cirrhosis. Eleven cirrhotic patients were studied twice while in balance on a 10 meq Na, 100 meq K diet: control and NI. The conditions of seated posture and time of day were identical. UNaV [Na excretion rate] was constant throughout C, ranging from 1-2 .mu.eq/min. During NI, UNaV increased progressively from 1 .+-. 1 (SEM) during the prestudy hour to 89 .+-. 32 .mu.eq/min during h 5 of NI (P < 0.02), greatly exceeding the comparable value found in normal subjects on an identical diet. The increase in UNaV was accompanied by a 2 to 3-fold increase in K excretion rate UKV (P < 0.001). In 7 patients restudied during chronic spironolactone (SPL) administration, SPL alone resulted in a modest increase in UNaV to 26 .+-. 7 .mu.eq/min. In contrast, during NI + SPL, UNaV increased from prestudy hour mean of 30 .+-. 9 to a peak mean of 147 .+-. 25 .mu.eq/min (P < 0.01). Despite SPL, the marked natriuresis was accompanied by an increase in UKV from prestudy mean of 39 .+-. 5 to a mean peak of 84 .+-. 13 .mu.eq/min (P < 0.005), strongly suggesting an enhanced distal delivery of Na. The decrease in UNaV of cirrhosis is attributable only in part to hyperaldosteronism; a diminished effective blood volue may participate in mediating the decreased UNaV of cirrhosis.