SummaryA method has been described for obtaining isolated human glomerular basement membrane. Evidence for the purity of the isolated GBM includes electron microscopic and chemical data. Some of the membrane constituents, in particular hydroxypro-line, aminosugars, sialic acid, neutral sugars, and lipids have been identified. Hexuronic acid is absent as is DNA. Sixty percent of the nitrogen of the membrane can be accounted for by collagen; the remainder may be contributed by the protein moiety of a glycoprotein species.The authors gratefully acknowledge the help of Dr. James B. Longley, Dept. of Anatomy, and Dr. G. R. Schrodt, Dept. of Pathology, in preparing the light microscopic and electron microscopic sections and photographs, and Dr. Charles Duncan, Dept. of Medicine, for his help in the thin layer chromatogra-phy of the lipids.