A new in vitro hormone-synthesizing cell system, line BeWO, derived from human gestational choriocarcinoma, has been permanently established; a high degree of synthesis of functional hormone has been maintained for 18 months in tissue culture. Predominantly glycolytic metabolism, dependent on the level of glucose in the medium, has been observed. Many facets of placental and tumor-cell metabolism, growth, and differentiation are found in this unique multipotential cell.