The loading of biocompatible matrices with growth factors offers the opportunity to induce specific cell behavior. The attachment of heparan sulfate (HS) to these matrices may promote the binding, modulation, and sustained release of signaling molecules. In this study, basic fibroblast growth factor (bFGF) was bound to crosslinked collagenous matrices with and without covalently attached HS. The tissue response to these matrices was evaluated after subcutaneous implantation in rats. Attachment of HS to collagen matrices increased the bFGF binding capacity threefold and resulted in a more gradual and sustained release of the growth factor in vitro. bFGF primarily was located at the matrix margins. In vivo, the presence of HS without bFGF resulted in a transient vascularization, predominantly at the matrix periphery. Angiogenesis was further enhanced by combining HS with bFGF. In contrast to collagen-HS and collagen/bFGF matrices, collagen-HS/bFGF matrices remained highly vascularized throughout the matrix during the 10-week implantation period. In addition, these latter matrices revealed an intense and prolonged tissue response and considerably promoted the generation of new tissue. Foreign body reactions were only observed sporadically at this time interval. It is concluded that bFGF loading of collagen-HS matrices has additional value for those tissue-engineering applications that require enhanced angiogenesis and generation of new tissue.