Growth/differentiation factors (GDFs) are members of the TGF superfamily (1,2). Members of the TGF superfamily are involved in embryonic development and adult tissue homeostasis (1). GDF-1 expression is almost exclusively restricted to the central nervous system and mediates cell differentiation events during embryonic development (3). Neither GDF-3 (Vgr-2) nor GDF-9 contains the conserved cysteine residue which is found in most other TGF superfamily members. GDF-3 is detectable in bone marrow, spleen, thymus and adipose tissue, whereas GDF-9 has only been detected in ovary (4). GDF-5 (also designated CDMP-1) has been shown to induce activation of plasminogen activator, thereby inducing angiogenesis. It is predominantly expressed in long bones during fetal embryonic development and is involved in bone formation. (5). GDF-5 mutations have been identified in mice with the mutation brachypodism (bp), a mutation which affects the length and number of bones in limbs (6). GDF-6 and GDF-7 are closely related to GDF-5 (6). GDF-8 has been shown to be a negative regulator of skeletal muscle mass (1).