To investigate the effects of angiotensin-converting enzyme (ACE) inhibitors on the cellular function and structure in a variety of organs during the aging process, one hundred CF1 mice were divided into four groups of 25 animals each. Groups A, B, and C received enalapril in drinking water from weaning until the age of 24 mo. Doses administered were (in mg/l): group A, 20; group B, 10; group C, 5. Group D is the control. Animals were killed, and morphometric studies were performed in heart, kidney, liver, and spleen. As a result, there was a decrease of renal and myocardial sclerosis and an increase in the number of mitochondria in heart and liver cells, which is associated with a significant increase in survival of animals receiving ACE inhibitors. These findings lead us to think that natural aging mechanisms have been altered in those animals.