A graded sieving procedure was used to isolate both glomeruli and tubules from renal cortex of cattle, pig, sheep, horse, man and rat. In addition, tubules from rabbit renal cortex were isolated. Glomerular and tubular basement membranes (GBM and TBM, respectively) were obtained with a detergent procedure. Purity of preparations was established with light and electron microscopy and by estimating total phosphorus content. Amino acid and carbohydrate compositions of the basement membranes were determined and statistically evaluated. Chemical composition of the preparations of all species was typical for renal basement membranes. Significant species-dependent variations were found, however, for many chemical constituents. Comparison of the chemical composition of GBM with TBM as pairs from individuals showed as a common phenomenon in all species that GBM preparations contain more of the heteropolysaccharide constituents, especially twice as much neuraminic acids than TBM preparations. Observed differences may be related to variations in immunogenic properties of the different types of renal basement membranes.