In this study, we have attempted to evaluate by immunohistochemistry assay the glomerular alpha smooth muscle actin (ASMA) expression in 53 kidney biopsy specimens obtained from patients with glomerular nephropathy as compared with 16 histologically normal human kidneys. An enhanced mesangial ASMA expression was observed in 26 of 53 specimens of patients with glomerulonephritis. In contrast, normal glomeruli showed no ASMA-positive mesangial cells. Furthermore, we have analyzed the specificities of antibodies eluted from kidney biopsy specimens from patients and controls using an enzyme immunoassay against a panel of self antigens composed of actin, myosin, tubulin and DNA. The antibodies eluted from exclusively renal biopsy specimens of patients with an enhanced glomerular ASMA expression showed high IgG activity restricted to actin. Our results demonstrated the presence of IgG anti-actin activity in glomerular nephropathy patients with an enhanced mesangial ASMA expression.