Blood pressure, plasma renin activity (PRA), sodium balance and hematocrit were measured before and a week after constriciton of the unilateral renal artery in rabbits. In some animals, urine flow and sodium output from both the constricted and the contralateral intact kidneys were estimated. Juxtaglomerular granulation index (JGI) and sodium content in renal tissue of both the constricted and the contralateral kidneys were also measured.<br>The following results were obtained.<br>1) Mean blood pressure was elevated from 113.3±7.6mmHg to 136.6±13.9mmHg by unilateral renal artery constriction. Elevation of mean blood pressure more than 25mmHg was obtained in 11 out of 20 animals. PRA was also increased to 5.16±2.63ng/ml/hr but the distribution of them was considerably wide.<br>2) A tendency of negative sodium balance was observed in unilateral renal artery constricted rabbits, which could be divided into two groups, animals with a negative sodium balance more than -1.50mEq/Kg/day (Group A) and the rest (Group B). The difference in sodium balance was due to the differences in both intake and output of sodium.<br>3) A significant positive correlation between mean blood pressure and PRA and negative correlations between sodium balance and each of mean blood pressure and PRA were observed in group A. A positive correlation between mean blood pressure and PRA was also detected but blood pressure rather closely correlated to sodium balance in group B. In many rabbits of group B, PRA was not increased but blood pressure was rather high as compared with group A.<br>4) There were no significant changes in hematocrit.<br>5) Sodium output was markedly decreased in the constricted kidneys while it was significantly increased in the contralateral kidneys.<br>6) JGI was increased to 72.0±37.8 in the constricted kidneys and decreased to 10.4±8.4 in the contralateral kidneys. A significant positive correlation between JGI of the constricted kidneys and PRA was detected.<br>7) Renal cortical sodium content was slightly decreased in both the constricted and the contralateral kidneys. Sodium content in the reanl medulla was decreased to 272.40±137.35mEq/Kg in the constricted kidneys and 266.86±116.06mEq/Kg in the contralateral kidneys. A significant positive correlation was detected between them. A significant positive correlation between renal medullary sodium content and JGI and a significant negative correaltion between medullary sodium content and sodium output in the contralateral kidneys were observed.<br>The results indicate that there are two types of hypertension, one of which is renin dependent one with negative sodium balance and the other is rather sodium dependent, which is present in acute stage of unilateral renal artery constriction.