1. The renal artery to a lone remaining kidney was constricted in fourteen concious dogs. The following variables were measured in all animals: blood pressure (BP), cardiac rate (CR), plasma renin concentration (PRC), plasma volume (PV), extracellular fluid volume (ECFV) and plasma non-protein nitrogen (NPN). Sodium balance was estimated in eleven dogs. Cardiac output (CO), total peripheral resistence (TPR) and stroke volume (SV) were measured in nine dogs. Angiotensin responsiveness (AR) was measured in six animals.
2. Within 2 hr the following changes occurred: a sharp increment of BP, PRC and TPR, with initial reduction or no change in CO and CR; SV and PV were not changed. The linear regression of BP changes on PRC changes did not differ statistically from the one previously obtained during the infusion of exogenous renin in the conscious dog. AR was much depressed at 2 hr.
3. After 24 hr a slight but significant sodium retention developed, while PV and ECFV and SV increased, CO remained unchanged owing to a decrease of CR. PRC tended to return toward normal while BP remained high. Thus the linear regression between these two variables disappeared. At this stage AR increased toward normal and in two dogs exceeded normal.
4. On days 3–4 and 6–7 after constriction, CO increased owing to a rise of SV, while TPR decreased. PV and ECFV were expanded while sodium balance was maintained. AR varied very much in the individual dogs according mainly to changes of PRC, sodium balance and PV.
5. On days 12–14 sodium balance became positive again, PRC returned within normal levels in almost all the dogs. PV and ECFV also tended to decrease to normal. CO and AR were measured in only two dogs at this stage.
6. It is suggested that the early rise of blood pressure might be produced by the increase of PRC, while 3–6 days after the constriction the expansion of PV with the increase of CO contributed to the maintenance of the hypertension.