Saiko is predominantly contained in Saireito, a Chinese herbal medicine. The present study was conducted to determine whether or not Saiko is involved in the inhibition by Saireito of nifedipine-induced proliferation and collagen synthesis in gingival fibroblasts. Nifedipine (10 μM) significantly enhanced the proliferation starting on day 5 of the culture period. When added together with nifedipine, Saiko at concentrations of 0.05%- 0.2% (w/v) dose-dependently inhibited the nifedipine-induced proliferation, and at the highest concentration tested (0.2%), Saiko inhibited the nifedipine-induced proliferation by about 40%. Moreover, Saiko (0.2%) also inhibited the normal proliferation at days 11 and 14. Sole application of nifedipine (10 μM) augmented the release of bFGF, and Saiko concentration-dependently reduced the level of bFGF in the nifedipine-containing culture medium. Nifedipine (10 μM) increased the production of type I collagen to almost twice that of the control (normal medium), and Saiko at concentrations above 0.1% significantly reduced the nifedipineinduced production of collagen. In conclusion, the present findings demonstrate that Saiko inhibited the nifedipine-induced proliferation of gingival fibroblasts by reducing the release of bFGF and that Saiko is involved in the Saireito-induced inhibition of nifedipine-stimulated proliferation and collagen synthesis in gingival fibroblasts.