Undifferentiated callus were induced from the young leaves of Taxus cuspidata by treatment with various combinations of plant growth hormones. The effects of light and culturing temperature on production of baccatin III, the precursor of taxol, were studied. The contents of baccatin III in the cultured callus were analysed by HPLC. The illumination of fluorescence and administration of isoleucine, one of the possible substrates in biosynthesis of terpenoids, to the culturing media increased the production of baccetin III.