The diagnosis of IgA nephropathy relies on the histologic demonstration of glomerular mesangial IgA deposits. However, only a very small fraction of IgA, namely, galactose-deficient IgA1, seems to induce the disease. So far, this type of IgA could only be detected using mass spectrometry or lectins, which are relatively difficult to standardize. A novel monoclonal antibody, KM55, specifically recognizing galactose-deficient IgA1, may now change this.