The glomerulus develops progressive injury with advancing age which is particularly pronounced in males and is not the result of any specific disease process. In the present studies conducted in rats, glomerular function and structure were examined in adult (8 mo), elderly (12 mo), and old (19 mo) Munich Wistar rats. Intact males and females and castrated rats of both sexes were studied to determine the role of the sex hormones in mediating age-dependent glomerular damage. Intact males developed glomerular injury and proteinuria whereas females, both intact and ovariectomized, and castrated males were protected from injury. Glomerular blood pressure did not increase with advancing age in any group and did not correlate with glomerular damage. Glomerular volume did increase with advancing age in all groups but did not correlate with glomerular damage. We found that the presence of the androgens rather than the absence of the estrogens provide the risk factor for development of age-dependent glomerular damage. Neither glomerular hypertension nor glomerular hypertrophy provide the primary mechanism by which age-dependent glomerular injury occurs in the intact male.