Abnormally high humoral responses have been described in IgA nephropathy (IgAN), towards antigens commonly involved in infectious events or food intolerance. Here we report a comparative analysis of humoral responses to a common environmental antigen, dextran B 512, present both in nonpathogenic microorganisms and normal diet. Dextran-specific IgG, IgA and IgM were assayed using an ELISA method in serum samples from 121 patients with IgAN, 40 controls and 32 patients with biopsy-proven renal diseases different from IgAN. Among the latter, 17 were transplant recipients. Anti-dextran IgG antibodies were found significantly (p < 0.05) more frequently and at higher levels in IgAN patients than in patients with other renal diseases. Anti-dextran IgA were at significantly (p < 0.05) higher levels in IgAN patients than in controls or untransplanted NIgAN patients. However, similarly elevated levels of anti-dextran IgA were found in IgAN patients and transplanted patients with other renal diseases. These data confirm that IgA and IgG responses towards common antigens are elevated in IgAN, possibly as a consequence of the pathogenesis of this disease rather than because of renal impairment. Moreover, since the same degree of dysregulation was noted in the control group of transplanted patients whose initial diagnosis was not IgAN, these data favour the hypothesis of a global dysregulation of the IgA system in IgAN, yielding enhanced humoral immune responses to possible pathogens and diet antigens.