IgA1 and IgA2 deposits in the renal glomeruli were studied in 29 biopsy specimens from 17 children with IgA nephropathy and 12 children with anaphylactoid purpura nephritis. IgA1 and IgA2 were detected with the indirect immunofluorescence method, using various combinations of dilutions of sheep antihuman IgA subclass antisera and fluorescein isothiocyanate conjugated rabbit antisheep IgG antiserum. The glomeruli of all the 29 specimens studied were strongly positive for IgA1, while only twelve specimens were positive for IgA2. Ten specimens without IgM deposits were all negative for J chain. These results indicate that the glomerular IgA deposits consist mainly of monomeric IgA1, with a minor share for IgA2. The serum IgA in normal individuals consists of about 90% IgA1 and 10% IgA2. Therefore, it was assumed that the serum IgA is deposited irrespective of subclass in the glomeruli of the patients with IgA nephropathies.