The present studies were designed to test the hypothesis that angiotensin II (ANG II) mediates nonosmotic thirst in animals fed the low-NaCl K-free diet by preventing the increased generation of ANG II using the converting-enzyme inhibitor, enalapril. Animals were fed either a control salt or low-NaCl K-free diet and were treated with or without enalapril. Water intake in rats fed the low-NaCl K-free diet increased more than twofold on day 3 and remained elevated over the 10-day period of study. Treatment with enalapril (40 mg.kg-1.day-1) 1) prevented the striking rise in plasma renin activity in rats fed the low-NaCl K-free diet, 2) led to complete blockade of the pressor response to a 50-ng injection of angiotensin I but not ANG II, 3) did not affect daily water intake in rats consuming the control salt diet, 4) did not reduce basal water intake in rats fed the low-NaCl K-free diet below values measured in control animals, and 5) did not abolish water intake in response to osmotic stimulation. However, enalapril treatment abolished the increase in water intake that occurs in animals fed the low-NaCl K-free diet. In a double crossover study using two groups of rats fed the low-NaCl K-free diet, enalapril prevented increased water intake in rats initially fed the low-NaCl K-free diet and rapidly inhibited increased water intake in rats fed the low-NaCl K-free diet after the high water intake had been established.(ABSTRACT TRUNCATED AT 250 WORDS)