AbstractTGF-β2 and -β5 have been purified from medium conditioned byXenopuscultured cells (XTC) and identified based on their N-terminal amino acid sequence analysis and biological activity. When applied in high concentrations,XenopusTGF-β2, like porcine TGF-β2, induces expression of mesodermal markers from culturedXenopusectodermal explants, whereas TGF-β5 is inactive in this assay. However, the TGF-β's could be separated from the major mesoderm-inducing activity present in XTC medium.XenopusTGF-β2 and -β5 are approximately equivalent to TGF-β1 in their abilities to inhibit the growth of mink lung CCL-64 cells, induce anchorage-independent growth of rat NRK cells, inhibit the proliferation and antibody secretion of human B-lymphocytes, and stimulate chemotaxis of human monocytes. These data establish the functional activity of TGF-β5 and suggest that more complex multicellular systems, in contrast to most isolated cells, discriminate between the different TGF-βs.