A monoclonal antibody, PHM 5, directed against human glomerular epithelial cells, was prepared after immunisation of a mouse with isolated human glomeruli and fusion of spleen cells with a mouse myeloma. Binding of antibody to isolated glomeruli was detected by radioimmune indirect binding assay, and specificity for glomerular epithelial cells was shown using a four-layer peroxidase-antiperoxidase technique applied to epoxy resin sections of the human kidney cortex. PHM 5 appears to detect a human-specific cell surface carbohydrate antigen not previously described, and can be used to identify epithelial cells in renal biopsy sections and in culture outgrowths of isolated glomeruli.