The aim of this study was to examine the incidence of different renal lesions in rheumatoid arthritis (RA) and to determine their relationships with the type of previous drug therapy and with the specific features of immune disorders. Ninety four patients, 84 (89.9%) females and 10 (10.6%) males) with RA whose mean age was 45.2 +/- 11.9 years and duration of the disease 7.5 +/- 6.5 years were examined. Most of them had degrees 2 and 3 PA (62.7 and 24.4%, respectively). Systemic manifestations were encountered in 60 (63.8%) patients. Eighty one patients took nonsteroidal antiinflammatory drugs (NSAID) continuously: 18 patients for a year, 32 for 5 years, 14 for 6 to 10 years, and 17 for over 10 years. All the patients underwent clinical, laboratory, and instrumental study of partial functions of the kidney. Immunological study involved solid-phase immunoassay of IgA and IgM rheumatoid factor, von Willebrand factor antigens (WF:Ag), C-reactive protein. The serum concentrations were measured by the Mancini method. Changes in urinalysis and/or signs of decreased glomerular and tubular functions were found in 69 (73.%) patients, 25 (26.6%) had arterial hypertension. Tubular dysfunctions were more common [31 (32.9%) patients]. Signs of early renal failure were detected in 20 (21.2%) patients. There were no cases of acute renal failure. Amyloidosis, glomerulonephritis, pyelonephritis were diagnosed in 5 (5.3%), 16 (17%), and 13 (13.8%) patients, respectively. The above renal lesions were concurrent in some patients. Renal lesion correlated with the progression and severity of RA, the presence of systemic manifestations, and age. There was no relationship of both 5- and 10-year use of NSAID to the symptoms of renal disease. The use of these drugs for over 10 years was concurrent with the signs of chronic renal failure and arterial hypertension. Analyzing immunological disorders showed an association of increased erythrocytic sedimentation rates and WF:Ag with amyloidosis, that of higher IgA concentrations with proteinuria and tubular dysfunctions. It is concluded that renal lesion is common in RA, there is a predominance of tubular interstitial changes. In rare cases nephropathy is characterized by a benign course and fails to result in uremia. The symptoms of renal diseases are largely associated with RA progression and severity and the patients' age. Prolonged continuous use of NSAID may contribute to the development of renal failure. Different immune mechanisms are involved in the pathogenesis of glomerular and tubular nephropathy in RA.