Serum immunoglobulins IgG, IgA, and IgM, serum complement components C3 and C4, circulating immune complexes, antinuclear antibodies, and rheumatoid factor were measured in 56 patients with rheumatoid arthritis (RA) and nephropathy (23 with mesangial glomerulopathy; 13 with membranous glomerulonephritis; and 20 with amyloidosis) and 35 patients with RA without nephropathy (controls). Renal immunofluorescence findings in patients with mesangial glomerulopathy were compared with the serologic data. There were no differences in the occurrence of rheumatoid factor, antinuclear antibodies, and circulating immune complexes and the concentrations of serum complement C3 and C4 between various RA nephropathy groups and controls. Serum IgA and IgM concentrations were significantly higher in patients with mesangial glomerulopathy and amyloidosis than in controls. In patients with mesangial glomerulopathy glomerular IgM, IgA, and C3 were the most prominent findings in immunofluorescence examination. The serum IgA concentration was significantly higher in those patients with mesangial glomerulopathy with mesangial IgA deposits than in those without (4.97 (SD 1.03) g/l v 2.07 (1.21) g/l). The highest serum IgA concentrations (5.08 (1.39) g/l) were seen in the four patients with IgA glomerulonephritis. The prevalence of IgA glomerulonephritis in the renal biopsy material of the patients with RA was 5%, which possibly differs little from that seen in the general population. The results suggest that circulating immune complexes may not have any major role in the pathogenesis of various nephropathy types in patients with RA, contrary to their role in most extra-articular manifestations of RA.