Five patients with glomerulopathy and glomerular fibrillary protein deposits similar to those of amyloid but lacking the Congo red tinctorial affinity characterizing amyloid were studied. Clinically, these patients had severe proteinuria and microscopic hematuria, in addition, 2 patients had hypertension and renal function impairment. 5 renal biopsies were evaluated by light microscopy (LM), immunofluorescence (IF), immunoperoxidase (IP) and electron microscopy (EM). LM: mesangioproliferative, membranous (late stage) and membranoproliferative (late stage) patterns were seen in 2, 1 and 2 patients respectively. IF & IP: granular deposits, mainly of IgG, C3 and kappa, lambda light chains were found in all cases, either in mesangium and/or capillary walls. EM: randomly distributed fibrils with a diameter approximately 21nm (the diameter of amyloid fibrils is about 9.5nm) were found in glomerular basement membrane and/or mesangium. The pathologic findings suggested a new clinicopathological entity differentiated from amyloidosis. The relatively homogeneous nature of the immunoglobulin in the immune deposits is the basis for the fibril formation.