The tissue examined with light microscopy consisted of a portion of renal parenchyma composed entirely of cortex and a separate fragment of adipose tissue. The profiles of up to 17 glomeruli were examined with light microscopy, an additional 12 glomeruli were examined for immunofluorescence, and 5 glomeruli were present in the plastic-embedded sections submitted for electron microscopy. Of these 34 glomeruli, a total of 14 (41%) were globally sclerotic. The remaining glomeruli showed a diffuse process characterized by a non-uniform, acellular mesangial matrix expansion and focal, non-uniform thickening of the capillary walls by an eosinophilic, amorphous material suggestive of amyloid. This material, confined to the glomeruli without involvement of the tubular basement membranes or extraglomerular blood vessels, was focally PAS positive and Congo red negative. Some non-atrophic tubules had thickened PAS positive tubular basement membrane. Silver stain showed focal areas of subepithelial spiking in the capillary basement membranes. Immunoperoxidase amyloid panel showed equivocal staining for amyloid P (precursor associated with most forms of amyloid and with fibrillary glomerulopathy) and negative staining for amyloid A and transthyretin (prealbumin). No cellular proliferation, inflammatory lesions or crescents were seen. The tubules showed focal atrophy and the interstitium contained focal collagen deposition, both in proportion to the degree of glomerular sclerosis. Focal interstitial lymphoplasmacytic chronic inflammation was also present. Several of the tubules contained proteinaceous hyalin casts. The intrarenal arteries present showed moderate fibrointimal proliferation with reduplicated elastic laminae, and the arterioles showed mural thickening, suggesting underlying arterial and arteriolar nephrosclerosis.