Abstract: Schizandrin B, one of the components isolated from Fructus Schizandrae, was found to have protective action on liver injury and to increase the weight of liver in mice. In order to elucidate the cause and implications of the liver enlargement by Schizandrirn B, some studies were carried out in mice. The results indicate that the content of water, protein, RNA, glycogen and total lipid per gram liver of the group given Schizandrin B was almost the same as those of the control group, but the amount of all these biochemical constituents markedly increased. The DNA content per gram liver decreased, although the total amount of DNA in whole liver was the same as that of the control.In partially hepatectomized mice, Schizandrin B was also shown to increase the protein, RNA and DNA contents as well as, mitosis of liver cells. In addition, Schizandrin B Was found to enhance-the incorporation of ¹⁴C-phenylalanine into liver protein, and to increase hepatic microsomal cytochrome P-450 and protein contents significantly. From these results, it may be concluded that Schizandrin B is'an inducing agent of drug metabolizing enzyme, and the enlargement of the liver caused by Schizandrin B is mainly, due to hypertrophy and to a lesser degree, hyperplasia. However, Schizandrin B is different from phenobarbital in the respectof inducing drug metabolizing enzyme. The difference is that phenobarbital also induced an increase of liver cell microsomal RNA and phospholipid contents. Besides, phenobarbital wasshown to be able to shorten the survival time of CC14-intoxicated mice, while Schizandrin B did not.