The blood pressure. renal function, baroreflex response of heart rate and noradrenaline (norepinephrine) pressor response were determined in conscious, normotensive, sodium-replete dogs that had received fosinopril. Oral administration of fosinopril at a dose of 1 mg/kg per day for 5 days decreased the systolic arterial pressure from 147.1 +/- 3 to 131.8 +/- 4.3 mmHg (p < 0.05) and the mean arterial pressure from 99.7+/- 3.9 to 87.5 +/- 2.8 mmHg (p < 0.05), while heart rate was unchanged. A study of the noradrenaline pressor response showed a tendency to alleviate the increased MAP by fosinopril treatment, although this was not significant. There were no significant changes in the sensitivity of the baroreflex response in HR, although the setpoint was reduced. After 7 days of fosinopril treatment, the glomerular filtration rate had increased by 18.5% (p < 0.05). The effective renal plasma flow tended to increase, leaving the filtration fraction unchanged. The renal vascular resistance was reduced by 11.3% (p < 0.05). Fosinopril caused a significant 41.5% increase in urinary excretion of Na+ (p < 0.05), along with an elevation of urinary excretion of K+ and Cl- . It is concluded that fosinopril can lower the blood pressure, reduce the noradrenaline pressor response and lower the cardiac baroreflex setpoint to noradrenaline. Oral administration of fosinopril for 7 days affects both the renal haemodynamics and electrolyte excretions in conscious, normotensive, sodium-replete dogs.