Aging in rats with intact kidneys is associated with changes in selective glomerular permeability to macromolecules resulting in proteinuria and progressive glomerular sclerosis. We have previously reported that angiotensin-converting enzyme (ACE) inhibition in Munich Wistar Fromter/Ztm (MWF/Ztm) rats resulted in a significant reduction of proteinuria, in respect to untreated animals, and that treated animals were protected against the development of glomerular sclerotic lesions. The present study was designed to establish whether ACE inhibition protects against glomerular injury in male Sprague-Dawley rats, which develop spontaneous proteinuria and glomerulosclerosis with age. The effect of ACE inhibition was tested when proteinuria was already present. Four-month treatment with the ACE inhibitor perindopril prevented the increase in systolic blood pressure, compared with vehicle-treated animals, and significantly decreased urinary protein excretion of aging rats. Partial protection of the development of glomerular sclerosis was also observed.