Renal biopsies were performed on 18 patients afflicted with moderately severe or severe rheumatoid arthritis ranging from 20 to 58 years in age and with minimal to mild urine abnormalities. No abnormality was found in 11 cases. Seven biopsies revealed minimal increase in mesangial cells and matrix on light microscopy with focal tubular atrophy in some. Electron microscopy showed slight increase in mesangium, presence of ‘deposits’ in the latter and epithelial cells and fusion of podocytes in several places. Microtubular structures were found in one case. Immunofluorescent studies were negative in all ca