Raised levels of IgA immune complexes were found in 13 of 18 children with Henoch-Schönlein purpura irrespective of whether they developed nephritis or not. In contrast, only those children who developed nephritis had raised levels of IgG immune complexes as well. In 2 children with nephritis, two discrete peaks of IgA complexes were found, corresponding to 4 x 10(5) to 8 x 10(5) and 2.5 x 10(6) to 4 x 10(6) daltons. IgG complexes were found only in the larger-molecular-weight peak. Such differences in immune complexes may underlie the different manifestations of this disease.