Activin A is a TGF-β family member that exhibits a wide range of biological activities, including regulation of cellular proliferation and differentiation, and promotion of neuronal survival. Elevated levels of Activin A in human colorectal tumors and in postmenopausal women have been implicated in colorectal and breast cancers, respectively. The biological activities of Activin A can be neutralized by inhibins and by the diffusible TGF-β antagonist, follistatin. Activin A binds to the two forms of activin receptor type I (Act RI-A and Act RI-B) and two forms of activin receptor type II (Act RII-A and Act RII-B). Activins are homodimers or heterodimers of different β subunits. They are produced as precursor proteins with an amino terminal propeptide that is cleaved to release the C-terminal bioactive ligand. Recombinant Human/Murine/Rat Activin A is a 26.0 kDa disulfide-linked homodimer of two βA chains, each containing 116 amino acid residues.