Antitumor effects of nine components of a herbal medicine, 'Sho-saiko-to', were investigated on human hepatoma cell lines (PLC/PRF/5, Hep-G2), human liver cells (Chang) and a human pancreatic cancer cell line (BxPC-3). The concentration of each component required for 50% inhibition of cell growth of PLC/PRF/5 cells was as follows: saikosaponin-d, baicalin, 20 micrograms/ml; saikosaponin-a, baicalein, 50 micrograms/ml; saikosaponin-b2, -c, ginsenoside-Rb1, -Rg1, glycyrrhizin, > 1000 micrograms/ml. Saikosaponin-a in 50-micrograms/ml quantities inhibited the cell growth and DNA synthesis of all the cell lines tested. These results indicate that 'Sho-saiko-to' includes potent antitumor components such as saikosaponin-a, -d, baicalin against human hepatoma cells as well as other human cell lines.