To obtain a better understanding of the mechanism of proteinuria in amyloidosis we investigated the ultrastructural distribution and pattern of arrangement of glomerular amyloid fibrils in 15 patients. Clinical data were correlated with the ultrastructural features and with the morphometric indices obtained from composite electron micrographs of whole glomeruli. The epithelial side of amyloid deposits showed spicules (discrete pointed bundles of fibrils) and apparent fraying which we termed tufts (ill-defined and diffuse expansion of fibrils). The extent of mesangial amyloid deposition and total GBM deposition did not correlate with proteinuria. Current data suggest the importance of partial detachment of epithelial cells in pathogenesis of proteinuria, which in turn correlates with distortion of amyloid fibrils, spicules and tufts.