Abstract: The collagenolytic activity of mammalian biologic fluids is assayed by obtaining a specimen of such fluid; applying the fluid to a collagen film bonded to a surface such as that of a glass slide; incubating the slide; washing the slide; staining the slide with a dye, and determining the extent of dissolution of the collagen film from the unstained areas of the slide. The slide is preferably prepared by blending insoluble collagen with a solution of HCl to form a dispersion; applying the dispersion to the slide surface; drying the slide; and baking the slide to cross-link the collagen and bond it to the slide surface. The dispersion applied to the slide contains collagen particles having sizes of at least 1 micron and preferably at least 20 microns. The assay procedure is particularly useful for the determination of the collagenase activity of gingival crevicular fluid (GCF), in which case the fluid specimen is obtained on an absorbent medium such as a filter paper strip.