We investigated the angiogenic response induced by acellular femoral matrices implanted in vivo on to the chick embryo chorioallantoic membrane (CAM), a useful model for such investigation. The results showed that acellular matrices were able to induce a strong angiogenic response, comparable with that of fibroblast growth factor-2 (FGF-2), a well-known angiogenic cytokine. The angiogenic response was further increased when exogenous FGF-2 or transforming growth factor beta-1 (TGF-beta1) was added to the matrices and inhibited by the addition of anti-FGF-2 or anti-TGF-beta1 antibodies. The response may be considered to be dependent on a direct angiogenic effect exerted by the matrices, and also in part by the presence of FGF-2 and TGF-beta1 in the acellular matrices.