In the present study we treated rats with N-nitrosodimethylamine (DMN) or D-galactosamine (GALN) to achieve increased circulating IgA levels in rats. GALN-treated rats showed a six-fold increase in serum IgA levels after the first intraperitoneal (i.p.) injection, whereas a 10-fold increase after a second i.p. injection of GALN was seen. DMN-treated rats showed a three-fold increase in serum IgA levels. No differences were observed in IgG and IgM levels between treated and non-treated rats. Sequential renal biopsies analysed by immunofluroescence exhibited mesangial deposits of IgA with different intensities of C3 deposition. Rats treated with GALN showed more IgA deposition in the kidney than DMN-treated rats. The IgA deposition together with C3 was more prominent in rats treated with GALN than in rats treated with DMN. The deposition of C3 together with IgA was associated with an influx of monocytes as detected by ED-1, an antibody directed against a rat monocyte marker. These studies provide evidence that an increase in serum IgA levels is associated with deposition of IgA in the kidney and that IgA has an inflammatory potential.