This book discusses the topic of naturally occurring phorbol esters. Chapters include; environmental hazards of diterpene esters from plants, multi-stage carcinogenesis and the biological effects of tumor promoters, review of the family euphorbiaceae, biosynthetic and chemosystematic aspects of the euphorbiacea and thymelaeaceae, non-diterpenoid constituents of euphorbiacea, macrocyclic diterpenes of the family euphorbiacea, phorbol: its esters and derivatives, the daphnane polyol esters, the ingenane polyol esters, and the biochemical mechanism of action of phorbol ester.