The role of a natriuresis in the protective effect of potassium against the development and maintenance of salt-induced hypertension was studied. Uninephrectomized rats showed average systolic pressures of 177 +/- 3 mm Hg after the 28 days of treatment with DOCA while receiving a 1% NaCl solution to drink. The supplements of 0.2 and 1% KCl solution could counteract the blood-pressure raising effect of NaCl in a dose-related fashion: The average pressures on day 28 at these dosages were 131 +/- 3 and 120 +/- 3 mm Hg, respectively. The cumulative sodium retention was significantly less in the KCl-supplemented rats than the DOCA-salt rats. Exchangeable body sodium (sodium "space") at weeks 1 and 4 was significantly increased in the DOCA-salt rats as compared to those in the vehicle-treated rats. But, the potassium supplement could reduce sodium "space" dose-relatedly in the DOCA-salt rats. Overall, there was a close correlation between the systolic pressures and sodium "space" at week 4 (r = 0.811, P less than 0.01). The results suggest that potassium may attenuate the rise in blood pressure during the DOCA-salt treatment in uninephrectomized rats, mainly as a result of inhibition of sodium retention, by increasing renal sodium excretion.