It has been recognized that alpha-fetoprotein (AFP), as an oncofetal antigen, re-expresses in large amounts in adult tumor cells and serves clinically useful purposes as a tumor marker assay. However, its biological activities are still far from clear. In the present study, the ability of AFP to stimulate tumor cell growth was observed by in vitro test system. The new finding indicates that AFP contributes to the generation and development of tumor and is an important target action site of tumor therapy.