A method is described for the isolation of large quantities of basement membrane from bovine renal glomeruli under conditions which minimize or prevent degradation by tissue-associated proteases. The method incorporates the use of moderately-high concentrations of the protease inhibitors: ethylenediamine tetraacetic acid, epsilon-amino caproic acid, N-ethymaleimide, and diisopropylfluorophosphate; and the maintenance of a temperature of 0-4 degrees C throughout the procedure. Glomeruli preparations are isolated by a modified sieving technique and are routinely of purity greater than 97%. Under optimum conditions, three to four grams of basement membrane can be isolated under safe and rapid conditions in one week.