A four-year-old male with steroid refractory nephrotic syndrome was found to have diffuse deposition of α2-macroglobulin (α2M) in the glomeruli which showed diffuse mesangial proliferation and partial hyalinization by light microscopy. Camostat mesylate, a commercially available synthetic proteinase inhibitor, led to biochemical and clinical improvement. Twenty-two patients with 7 biopsy-proven renal diseases did not have any deposition of α2M in their kidney tissue. Though the pathogenetic mechanism is unknown, this is probably the first report of the deposition of α2M in renal tis