A study on the deposition of complement control proteins in renal tissues from patients with IgA nephropathy is described. Renal biopsy specimens were obtained from patients with IgA nephropathy and other glomerular diseases. These biopsy samples were stained with antisera to human C4-binding protein and beta 1H globulin by indirect immunofluorescent staining. It was shown that the complement system is activated in IgA nephropathy via the both alternative and classical pathways.