We have purified to near homogeneity a novel 17 kD growth factor from bovine uterus which we designated heparin-binding growth factor-8 (HBGF-8). The growth factor binds tightly to cation exchange resins and to Heparin-Sepharose and is stable to acetone precipitation and labile in acid. Based upon total activity in acetone extracts of bovine uterus stimulating 3H-thymidine incorporation into DNA of serum-starved NIH 313 cells, a 6940 fold purification was achieved with an overall yield of HBGF-8 activity of 0.4%, using extraction of acetone powders and chromatographic separations at neutral pH. Approximately 18 micrograms protein was obtained from 1.2 kg wet weight of tissue. HBGF-8 was clearly separated from 17.5 kD bovine uterus basic fibroblast growth factor (bFGF) by purification and its N-terminal amino acid sequence analyzed. A polypeptide with a unique 25 N-terminal amino acid sequence was found. HBGF-8 was as active as acidic fibroblast growth factor (aFGF) and slightly less active than bFGF in the mouse NIH 3T3 fibroblast mitogenic assay system with an intrinsic specific activity of 5000 dpm/ng under standard assay conditions.