Specific tissue interactions between epithelia and mesenchyme (or stroma), e.g., epithelial-mesenchymal (or -stromal) interactions mediate crucial aspects of normal development and tissue regeneration. These events affect tissue induction, organogenesis, cell movement, and morphogenesis of multicellular structures. Extensive and diverse studies have established that hepatocyte growth factor (HGF), a ligand for the c-met protooncogene product of receptor tyrosine kinase, is a mesenchymal- or stromal-derived multipotent polypeptide which mediates epithelial-mesenchymal interactions. During embryogenesis, HGF supports organogenesis and morphogenesis of various tissues and organs, including the liver, kidney, lung, gut, mammary gland, tooth, skeletal system, etc. In adult tissues, HGF elicits a potent organotrophic function which supports regeneration of organs including the liver, kidney, and lung. In the brain, HGF is a new member of the family of neurotrophic factors. In neoplastic tissue, HGF is involved in tumor invasion and metastasis, through tumor-stromal interactions. While HGF was originally identified as a potent mitogen for mature hepatocytes, the biological functions of this factor reach far beyond the original identifications. Such being the case, use of HGF for purposes of therapeutics is being given increasing attention.