The Fibroblast Growth Factors (FGFs) are heparin binding glycoproteins that exert a variety of biological activities toward cells of mesenchymal, neuronal, and epithelial origin. FGF10 belongs to the subgroup of FGFs that also includes FGF3, 7, and 22 (1). Mature mouse FGF10 is an approximately 20kD protein that contains a serinerich region near its Nterminus (2, 3). C terminal to this region (aa 62 209), it shares 94% and 100% amino acid sequence identity with human and rat FGF10, respectively. FGF10 is secreted by mesenchymal cells and associates with extracellular FGFBP (1, 4). It preferentially binds and activates epithelial cell FGF R2 (IIIb) and interacts more weakly with FGF R1 (IIIb) (5). The mitogenic and chemotactic properties of FGF10 are critical in many tissues during embryogenesis. This includes limb bud initiation (6), palate development (7), branching morphogenesis and directional outgrowth of lung buds (2, 8), formation of the otic vesicle and chochlea (9), adipogenesis (10), and the development of prostate, mammary, lacrimal, and submandibular salivary glands (11 14). FGF R2 (IIIb) signaling in these responsive tissues is similarly important during embryogenesis (7, 9, 12 14). The expression and function of FGF10 are negatively regulated by Shh and BMP4 in the developing lung (2, 8). Overlapping expression patterns and activities with FGF3, 7, and 8 suggest at least a partial redundancy in FGF10 biology (7, 9, 13, 14). FGF10 induced signaling through FGF R2 (IIIb) also contributes to the progression of pancreatic cancer (15).