Abstract: An assay for detecting microbial protease activity in clinical and laboray samples is described which comprises gathering a sample suspected of containing certain microorganisms having the desired protease activity; immobilizing the microorganisms in the sample on a solid phase substrate; contacting the immobilized microorganisms with an enzymatic substrate producing an enzymatic substrate end-product; contacting the enzymatic substrate end-product with a chemical enhancing reagent producing a detectable chromogenic reaction which varies in intensity with the level of protease activity in the sample; and detecting the chromogenic reaction whereby the semi-quantitative presence of the protease activity in the sample is determined.