The role of renal biopsy in 46 patients with end stage renal failure was assessed. Renal tissue was obtained by open renal biopsy in 24 patients, by needle biopsy in 5, and at bilateral nephrectomy in 17. In 4 patients the renal biopsy specimens showed advanced changes that could only be diagnosed as "end stage kidney." In 42 patients (91 per cent), a precise renal diagnosis was made I n 20 patients (43 per cent) the prebiopsy clinical impression differed from the histologic diagnosis. In the 29 patients undergoing renal biopsy, minor postoperative morbidity occurred in 5. We conclude that a renal biopsy in patients with end stage renal failure will result in a change in clinical diagnosis in a significant number of patients and can be performed with low morbidity.