Some antitumor activities of component (E), extracted from the root of Fagopynum Cymosum (Trev) Meisn (FCTM), have recently been discovered in vivo and in vitro. The component E (CE)'s pattern of action with tumor cellular DNA at the molecular pharmacological level was investigated by macromolecular synthesis experiment (MSE) and human DNA interaction system established in our laboratory. The experiments demonstrated that, in vitro, the agent could markedly inhibit the incorporation of3H-TdR into the cellular DNA, and the IC50 in P388 leukemia cell and in SGC-7901 cell was 17.86 μg/ml and 110.4 μg/ml, respectively. The agent, at mg/ml level, 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 action changed to intercalation irreversible pattern. According to these observations, the authors infer that CE 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 CE with those of componen's (CB3 and CD1), extracted from FCTM by the same methods, and found that CE is the most active agent against the DNA of cancer cells among the extracts from FCTM. © 1989 Chinese Journal Of Cancer Research.