A total of 234 patients with chronic glomerulonephritis, detected on the basis of clinical, immunological and pathomorphological criteria, have been examined. A group of 23 chronic glomerulonephritis patients with massive deposits of immunoglobulin A found by immunofluorescent examination, has been separated on the basis of immunohistochemical studies. In this group, occurrence of different morphological forms of glomerulonephritis has been observed: 30.4% mesangial-proliferative glomerulonephritis, 13% submicroscopic glomerulonephritis and one case of membranous glomerulonephritis. Complete haemolytic activity of complement, level of complement components C3 and C4, immunological complexes circulating in blood, properdin and immunoglobulin A levels, fibrin and fibrinogen (FDP) degradation product concentrations and their 24-hour excretions with urine have been determined. Preliminary observations of this group of patients seem to indicate a positive effect of steroid therapy in glomerulonephritis with IgA deposits, irrespective of the morphological form of the disease.