On the surface of smooth muscle cells there are two types of receptors for the mitogenic and angiogenic growth factor fibroblast growth factor-2 (FGF-2); a high affinity tyrosine kinase FGF receptor (FGFR1) and low affinity heparin./heparan-like glycosaminoglycan (HLGAG) component of surface expressed proteoglycans. It is believed that all three components; FGFR1, FGF-2, and the HLGAG chains, must form a ternary complex for maximal cellular stimulation. To carefully examine the role surface HLGAGs play in FGF-2-mediated proliferation of SMCs we have utilized HLGAG degrading enzymes heparinase I, II and III. We report that heparinase treatment of bovine smooth muscle cells inhibits the binding of (125)I-FGF-2 to FGFR1, but does not inhibit FGF-2 induced cellular proliferation. Through the use of both sodium chlorate and FGF-2 mutants with deficient HLGAG-binding capabilities, we show the FGF-2-HLGAG interaction is important for FGF-2's ability to induce SMC proliferation. Finally, we report conditioned media from heparinase treated SMCs is capable of supporting FGF-2 induced proliferation in an HLGAG-free lymphoid F32 cells, suggesting that the heparinase generated fragments are responsible for the proliferative response. The data presented here suggest FGF-2 is capable of stimulating smooth muscle cell proliferation through an FGFR independent, HLGAG dependent mechanism.