In the embryonic development of vertebrate, sequential cleavage is followed by the gastrulation as the first dynamic event of morphogenesis. Mesodermal induction is the most important event for normal body patterning such as the gastrulation, neural induction and formation of various organs. In the study to search for the mesodermal inducing factor, we reported "activin" as a strong mesoderm-inducible factor by the "animal cap assay", the in vitro assay system using amphibian pluripotential cell mass. We found that activin has mesodemal and endodermal inducing activity in dose-dependent manner, and then established the invitro induction system for various types of tissues and organs including craniofacial cartilage from animal cap cells by the treatments with activin and other inducing factors. Embryonic transplantation method showed that the treatments of animal cap cells for the induction of pronephros, beating heart were able to induce normally functional organs in vitro. These in vitro induction methods are useful for investigation of the molecular mechanisms of organ formation and body patterning in vertebrate development.