The effects of repeated administration of quinapril (10 mg/kg/day) on the development of hypertension, cardiac hypertrophy and survival rate were examined, and compared with those of enalapril (10 mg/kg) in salt-sensitive Dahl (Dahl S) rats and 1% saline-loaded stroke-prone spontaneously hypertensive rats (SHRSP). The Dahl S rats were treated with the drugs at 10 to 20 weeks of age and the SHRSP, at 8-19 weeks of age. (1) In the Dahl S rats, salt loading rapidly raised systolic blood pressure, which was around 220 mmHg at 10 weeks of age. Both quinapril and enalapril significantly prevented the development of hypertension (below 160 mmHg) and cardiac hypertrophy. Age-associated histopathological alterations in the kidney and mesenteric artery in Dahl S rats were suppressed by the drug treatment. (2) Salt-loaded SHRSP rapidly developed severe hypertension (270 mmHg at 12 weeks of age) accompanied with stroke signs, and 19 animals out of 20 died by the end of the experiment. Both quinapril and enalapril significantly inhibited the age-associated development of hypertension and markedly improved the survival rate (only two animals out of 16 died in both groups). These results suggest that quinapril has protective actions against age-associated development of hypertension and cardiac hypertrophy, and as a result, it prolongs the life span.