The extraction and isolation of 2 active cocarcinogenic agents from the seed of Croton
tiglium L. and their long-term biologic testing are described. Both materials are po
tent cocarcinogens at very low dosages. The biologic activity of chemically trans
formed derivatives of the active materials is also reported. Phorbol myristate acetate,
a semisynthetic compound derived from croton resin, showed notable promoting activ
ity. Some aspects of the chemistry of the active materials are discussed.