A sensitive assay for type IV collagen degradation using an avidin-biotin sandwich technique is described. Biotinylated type IV collagen is allowed to bind to an avidin-coated microtiter plate. The solution to be assayed is incubated with the biotinylated collagen bound to the avidin plate. Collagen degraded by the solution is released into the supernatant and transferred to a second plate coated with avidin. By addition of biotinylated horseradish peroxidase to this second plate, the amount of collagen degraded is determined. Our assay requires only 0.5 microgram of type IV collagen per microtiter plate and detects nanogram quantities of bacterial collagenase activity.