The present invention relates to huXAG-1, huXAG-2 and huXAG-3 proteins which are novel human growth factors. In particular, isolated nucleic acid molecules are provided encoding the huXAG-1, huXAG-2 and huXAG-3 proteins. huXAG-1, huXAG-2 and huXAG-3 polypeptides are also provided as are vectors, host cells and recombinant methods for producing the same. The invention further relates to screening methods for identifying agonists and antagonists of huXAG-1, huXAG-2 or huXAG-3 activity. Also provided are diagnostic and therapeutic uses of huXAG-1. huXAG-2 and huXAG-3.