In order to demonstrate the diagnostic value of serum IgA-fibronectin (FN) aggregates in IgA nephropathy, serum samples from 91 patients with IgA nephropathy, 14 patients with Henoch-Schonlein purpura, 117 patients with non-IgA nephritis, 24 random in-patients and 234 normal controls were examined for IgA-FN aggregates by using ELISA. The results showed that the level of IgA-FN aggregates increased markedly in the serum of patients with IgA nephropathy and 61.5% of them reached the positive standard. Only 8.8% of the patients with non-IgA nephritis, none of the in-patients with non-renal diseases and 5.1% of the normal controls were beyond the positive criteria. But the level of IgA-FN aggregates were also elevated in the serum of patients with Henoch-Schonlein purpura and lupus nephritis. These data indicate that serum IgA-FN aggregates may be useful in the diagnosis of IgA nephropathy, but Henoch-Schonlein purpura and lupus nephritis should be ruled out.