Renal biopsy specimens from 39 patients with rheumatoid arthritis and clinical signs of renal disease disclosed a mild mesangial glomerulopathy in more than 1 in 4 cases. Almost all patients had deposits of immunoglobulin and complement in the mesangial lesions. This type of glomerulopathy was the most common cause of hematuria and was also frequently encountered in proteinuric patients. Clinically it was not possible to distinguish between mesangial and membranous nephropathy.