Acute or chronic inhibition of angiotensin converting enzyme (ACE) activity in normotensive rats may increase, decrease or cause no change in renal blood flow. Since renal blood flow and the glomerular filtration rate are highly dependent on protein intake, we investigated the question of whether the reported differences in the renal effects of ACE inhibition can be explained by the level of food intake. Glomerular filtration and arterial pressure were measured in conscious, chronically catheterized rats, which were either fed or fasted for 24 h on the day of experiment. In the control group, the glomerular filtration rate was 45% higher in fed than in fasted rats, while blood pressure and plasma renin concentration were unchanged. In experimental animals, given daily 1-mg/kg doses of the ACE inhibitor perindopril, the glomerular filtration rate was the same in both fed and fasted animals and comparable to the values of fasted control animals. Mean blood pressure was reduced from 113 to 91 mmHg by perindopril. It is concluded that chronic ACE inhibition prevents postprandial hyperfiltration and decreases the blood pressure of fed or fasted rats by 20 mmHg, but does not affect renal function in fasted rats.