Effects of a high-salt diet on blood pressure, extracellular fluid volume, and the renin-angiotensin system in rats with the two types of Goldblatt hypertension were examined. Both in one-kidney, one clip (1K1C) rats and in one-kidney, sham-clipped (1K) rats, systolic blood pressures of rats which received a high-salt diet for 4 weeks were higher than those of rats of respective groups on a normal-salt diet, suggesting an increased sensitivity of blood pressure to changes in salt intake. Whereas sodium space was increased in 1K rats on the high-salt 1K1C rats receiving the high-salt did not have significantly increased sodium space. These results suggest that acceleration of 1K1C hypertension with salt load could not be explained only by changes in extracellular fluid volume. In contrast, both in two-kidney, one clip (2K1C) rats and in two-kidney, sham-clipped (2K) rats, the high-salt diet produced no change in blood pressure despite the increase in sodium space, suggesting a decreased salt sensitivity. Although on the normal-salt diet the blood pressure of 2K1C rats tended to correlate with plasma renin activity, on the high-salt diet plasma renin activity was markedly decreased, and then blood pressure highly correlated with sodium space. Accordingly, the lesser salt sensitivity in 2K1C rats is probably attributable to the counterbalance of the suppressed renin-angiotensin system against volume expansion. Evidence presented suggests, therefore, that 1K1C rats have greater salt sensitivity of blood pressure than 2K1C rats.(ABSTRACT TRUNCATED AT 250 WORDS)