Some antitumor activities of component (E), extracted from the root of Fagopynum Cymosum (TreV) meisn (FCTM), have recently been discovered in vitro and in vivo. The component (E)'s pattern of action with tumor cellular DNA at the molecular pharmacological level was investigated by macromolecular synthesis experiment (MSE) and human DNA interaction HDI system established in our laboratory. The experiments demonstrated that, in vitro, the agent could markedly inhibit incorporation of H3-TdR into the cellular DNA, and the IC50 in P388 and SGC-7901 was 17.86 micrograms/ml and 110.4 micrograms/ml, respectively. The agent, at level of mg/ml, could produce an intercalation reversion pattern with DNA within a short time (2 hours). But when the interval was prolonged for over 4 hours, the pattern of action changed to intercalation irreversible pattern. According to these observations, the authors infer that component (E) interacts with DNA in two ways-directly and indirectly. The indirect action, especially in low concentrations, probably plays the major role. The authors have also compared the interaction of component (E) with those of components (CD1) and (CB3) extracted from FCTM by the same method and found that component (E) is the most active agent against the DNA of cancer cells among the extracts from FCTM.