Clusters of deeply staining "embryonal-type" epithelial cells surround hyaline glomeruli in some patients with end-stage renal disease treated with dialysis. The kidneys of 40 patients, dialyzed for 2 months to 2 years, were studied with a variety of histologic and histochemical staining techniques. In 4 of these cases such "embryonal-type" cell clusters, arising from the parietal epithelium of Bowman's capsule and here termed "embryonal hyperplasia of Bowman's capsule epithelium" (EHBCE), are identified. In 6 additional cases there are similar cells in a tubular pattern, resembling the adenomatoid or pseudotubule structures of chronic, cresentic glomerulonephritis. The largest lesions are often found in groups within localized areas of cortex, giving their distribution a "field" effect. In such cases they have the appearance of new growths, suggesting the induction of a less differentiated cell type in these diseased adult tissues.