Effect of exogenously added soybean phosphatidylinositol on c-myc gene expressed and unexpressed human cancer cell lines was investigated. When phosphatidylinositol liposomes were introduced into culture media, viability of c-myc unexpressed cells was reduced, while that of c-myc expressed cells was not. Death of c-myc unexpressed cells by phosphatidylinositol liposomes was found to be caused by abnormally accumulated intracellular Ca2+, and it seemed to be related to reduction of protein kinase C activity.