Fractions of rib cartilage were obtained by homogenization and extracted with 4 M guanidinium chloride, and the washed residue was digested with purified collagenase. Differential centrifugation of the insoluble residue from this digestion yielded a non-collagenous fraction that earlier work had shown to contain microfibrils. This material contains a much higher concentration of epsilon(gamma-glutamyl)lysine than the ribs or any of the other cartilage fractions. This transglutaminase-derived crosslink may be a common component of extracellular matrix microfibrils.