Two HLA identical brothers with mesangial IgA glomerulonephritis are reported. Patient 1 developed gross hematuria at age 12 and required chronic hemodialysis at age 20. Patient 2 presented at age 21 with gross hematuria and normal renal function, the follow up period is only 9 months. Neither of these patients had nerve deafness, ocular defects or complement abnormalities. The family history did not support a diagnosis of classical hereditary nephritis, but a genetic linkage is strongly suggested by the identical HLA phenotypes of these brothers (A10 - A32 - B13 - B35). The B35 antigen has previously been suspected to be linked to this disease. These observations strongly support the hypothesis of an aberrant, genetically controlled, immune response, in patients with mesangial IgA glomerulonephritis.