Abstract: Aim To observe the effect of isoflavones on the growth of YAC-1 cells in vitro and ESC tumor in mice and their immune function. Methods Isof lavones induced inhibitory rate of YAC-1 cells and the proliferation of lymphocy te were assessed by the modif ied MTT assay.NK cell activities were determined by LDH.The anti tumor activity in vivo was observed by weighing the tumor and calculating spleen and thymus indexes.Results The grow th of YAC-1 cells were inhibited by isof lavones in a concentration and time-dependent manner.Isof lavones power ext racted from soybean (50, 100, 400 mg·kg^-1, o ral administ ration) could enhance spleen index and ConA-induced proliferation of lymphocyte in female mice, but not in male ones.Isoflavones in the doses of 50, 100, 400 mg·kg^-1 could significant ly inhibit spleen index and increase NK cell activi ties.The grow th of tumor was significant ly inhibited in ESC tumor-bearing female mice in the doses of 100, 400 mg·kg^-1.Conclusion Isof lavones has inhibitory effect on the growths YAC-1 cells in vi tro and ESC tumor in vivo.Isoflavones not only strengthens the nonspecail immune function of tumor-bearing mice, but also of the normal female mice.

Key words: isoflavones, genistein, daidzein, tumor, immune function