Since at least 1500 Be plants and plant extracts have been recognized as having anticancer activities (1). Surveys by Hartwell (2, 3) listed at least 3000 species so used. However the rational, organized study of plants as sources of potential an­ tineoplastic agents probably commenced with the pioneering studies of Hartwell et al (4-8) during the period 1947-1953 in which for the first time pure plant constit­ uents were isolated, characterized, and associated with the antitumor activity of the crude plant extract.! This review presents a critical appraisal of the current status of plant antineoplas­ tic agents, with particular emphasis on chemical structure and the significant fea­ tures (where known) that are required for antitumor activity. This review deals only with plant antineoplastic agents of high activity against mouse leukemia and mouse and rat solid tumors as defined by the National Cancer Institute (9). All ofthe plant antitumor agents covered have excellent antitumor activity in one or more rodent tumor or leukemia systems combined with reasonable therapeutic indices so that the agents are either in clinical testing or scheduled for such studies. As a consequence, many substances with marginal activity or with high toxicity are not included in this review. Material covered in earlier reviews (1, 10) is not discussed unless additional information has become available since the time of the previous review.