Human Long-R3-IGF-I is an analog of human IGF-I that has been engineered to increase biological activity. It is significantly more potent than human IGF-I in vitro due to decreased binding to IGF binding proteins. The recombinant human Long-R3-IGF-I has a calculated molecular mass of 9111Da and is expressed in E. coli. It is available in 100μg/vial, 500μg/vial, and 1mg/vial formulations and should be stored at 2-8oC for two years or -20oC for long term storage. Quality control tests show that it has a purity of >95% by RP-HPLC analysis and >98% by SDS-PAGE analysis, and a specific activity of 1.0×106 IU/mg as determined by the dose-dependant proliferation of murine BALBC 3T3 cells. Endotoxin levels are less than 1.0 EU per mg as determined by the LAL method.