We investigated the effects of CP-2 extracted from the mixture of Copis and Croton tiglium L, which showed very high cytotoxic effect to the various tumor cells, on the growth and steroidenesis of primary and transformed cell lines PA-GS6 and PO-GRS1 by cotransfectionwith SV40 and Ha ras oncogenes. CP-2 inhibited the growth of PA-GS6 and PO-GRS1 in a dose dependent manner when the growth of them was measured by cell number and by protein content, while CP-2 did not affect the growth of primary granulose cells. Productions of progesterone ofprimary and transformed granulosa cells were stimulated by forskolin, but this stimulatory effect was blocked by treatment of CP-2. Clinical application of CP-2 asa new anti-cancer drug and utilization of transformed granulosa cells as a model system for the screening of anti-cancer drug were also discussed.