Bone Morphogenetic Protein 5 (BMP-5) is a member of the structurally and functionally related bone morphogenetic proteins (BMPs) which constitute a novel subfamily of the transforming growth factor β (TGF-β) superfamily. In agreement with a possible role in the control of cell death, BMP-5 exhibited a regulated pattern of expression in the interdigital tissue. Transcripts of BMP-5 and BMP-5 protein were abundant within the cytoplasm of the fragmenting apoptotic interdigital cells in a way suggesting that delivery of BMPs into the tissue is potentiated during apoptosis. Gain-of-function experiments demonstrated that BMP-5 has the same effect as other interdigital BMPs inducing apoptosis in the undifferentiated mesoderm and growth in the prechondrogenic mesenchyme. BMP-5 is a member of the 60A subgroup of BMPs, other members of which have been shown to stimulate dendritic growth in central and peripheral neurons. The signaling pathway that mediates the dendrite-promoting activity of BMP-5 may involve binding to BMPR-IA and activation of Smad-1, and relative levels of BMP antagonists such as noggin and follistatin may modulate BMP-5 signaling. Since BMP-5 is expressed at relatively high levels not only in the developing but also the adult nervous system, these findings suggest the possibility that BMP-5 regulates dendritic morphology not only in the developing but also the adult nervous system. BMP-5 may play important roles not only in myocardial differentiation but also in the formation and maintenance of endocardial cushion tissue. Additionally, a high expression level of BMP-5 has been detected in certain tumors of mesenchymal origin.