Decorin is a small leucine-rich chondroitin/dermatan sulfate proteoglycan reported to interact with ®brillar collagens through its protein core and to localize atdandebands of the collagen ®bril banding pattern. Using a solid-phase assay, we have determined the interaction of peptides derivedbyCNBr cleavage of type I and type II collagenwith decorin extracted from bovine tendon and its protein core and with a recombinant decorin preparation.