1. The basal blood pressure and the drug-stimulated pressor response were studied in male offspring in the sixth generation (5d-PTx-F6) of rats parathyroidectomized on day 5 of pregnancy. 2. The systolic blood pressure in conscious 5d-PTx-F6 rats measured by a tail cuff was significantly higher (P less than 0.001) than in control rats. 3. Venous plasma renin activity was significantly lower (P less than 0.001) in the 5d-PTx-F6 rats. Plasma levels of calcium, sodium, and potassium in the 5d-PTx-F6 rats and in the controls did not differ. 4. Systolic arterial pressure response to intravenously (i.v.) administered angiotensin II (150 ng/kg) in the 5d-PTx-F6 rats was significantly greater than in the controls (P less than 0.05), when blood pressure was measured directly through a pressure transducer under anaesthesia. 5. Pressor responses to norepinephrine (5 micrograms/kg, i.v.) in the 5d-PTx-F6 rats were significantly lower (P less than 0.05) than in the controls, when blood pressure was measured directly under anaesthesia. 6. The findings suggest that the 5d-PTx-F6 rats undergo functional alterations of the renin-angiotensin and sympathetic nervous systems for cardiovascular regulations.