A subset of subjects underwent percutaneous kidney biopsy at the end of the treatment period to determine whether treatment with losartan was associated with structural differences. Baseline kidney biopsies were not performed because of safety concerns. Tissue was processed and embedded in epoxy resin (Epon 812) and prepared for microscopy as described previously (12 (link)). Light and electron microscopy were performed either in the Beckman Center for Electron Microscopy at Stanford University or in the Division of Nephrology at the University of Minnesota. Digital light and electron micrographs were used to make measurements using formal stereologic methods to account for two-dimensional sampling of three-dimensional objects (13 ). Predefined morphometric variables included glomerular volume, percent globally sclerotic glomeruli, fractional interstitial area, mesangial fractional volume, filtration surface area density, glomerular basement membrane width, number of endothelial cells, mesangial cells and podocytes per glomerulus, filtration slit frequency, and foot process width (12 (link),14 (link)–16 (link)).