Epidermal growth factor (EGF) and its receptor (EGF-R) were identified by immunohistochemical method (4 layer PAP) in the renal tissue specimens obtained from 11 normal kidneys and 17 cases of acute renal failure (ARF). The quantitative EGF and EGF-R in the tissue were expressed as positive tubules per mm2. The amount of EGF and EGF-R in renal tissue was markedly increased in cases of ARF than in normal persons. Positive EGF staining was present only in distal tubules, but absent from glomeruli in normal persons. In ARF patients EGF was identified in both distal and proximal tubules. It was also seen in the glomerular mesangial area in 2 cases complicated by mesangial proliferative GN. However, no obvious difference was noted in the distribution of EGF-R between normal and ARF specimens. The amount of EGF in the renal tissue varied with the morphological changes in tubules and the time when the renal biopsy was being taken. The amount of EGF was large in those with a Scr value less than 2.5mg/dl There was a more profound expression of EGF during the recovery from ARF.