Abstract: The present invention provides methods and compositions for modulating FGF-signaling and activities associated therewith, such as mitogenesis and angiogenesis. In particular, the invention provides crystal structure coordinates for a ternary complex of an FGF receptor, and FGF ligand, and a third compound, sucrose octasulfate, that binds to the FGF receptor and ligand to promote formation and dimerization of the ternary complex. Screening methods are provided by which novel agonists and antagonist for FGF-mediating signaling and activities may be identified using these crystal structure coordinates. Exemplary compounds are also provided that have novel utilities as agonists or antagonists of FGF-mediated signaling and activites.