FGF-9 is a heparin-binding growth factor belonging to the fibroblast growth factor (FGF) family. FGF-9 was first identified as a secretory protein from the human glioma cell line NMC-G1 and is reported to be widely expressed in rat brain. In the central nervous system, FGF-9 acts as an autocrine and a paracrine growth factor that is required for the development, growth, and survival of neuronal cells. During prenatal stages, FGF-9 expression is crucial for normal lung and airway development. FGF-9 null mutant mice show the phenotype of severe lung hypoplasia, which results in perinatal death. FGF-9 is key in stimulating cell proliferation after arterial, skeletal, and hepatic injuries. FGF-9 is also involved in tumorgenesis, enhancing transformation and progression of several malignant diseases, including prostate, lung, and colon cancer.