The paper presented here provides evidence of cytotoxicity to mouse 3CL-8 cell of friendcrythrocyte bY 50% Isatis tinctoria injection. In vitro this extract of traditional Chinese medicine exerts a strong cytostatic effect directly on mousc 3 CL-8 cell in tissue culture at a minimum concentration of 1 ∶80 dilution. In vivo, when injected subcutaneously aud locally ontumor site, it showed some cytotoxic effect on 3 CL-8, but showed no significant cytotoxiceffect intrapertoneally.