The antitrypanosomal activity of traditional Chinese herbal medicines and these crude drug ingredients were determined using axenic cultured bloodstream forms of Trypanosoma b. rhodesiense which is one of the two causative agents of African sleeping sickness in man. The drugs tested were 8 traditional Chinese herbal medicines and these 14 crude drug ingredients. Of these traditional Chinese medicines examined, san'o-shasin-to and oren-gedoku-to showed most potent antitrypanosomal effect. The minimal effective concentration (MEC) which killed all bloodstream form populations within 24 hours of both drug exposure was 125 microg/ml. The 50% effective concentration (EC50) of san'o-shashin-to and oren-gedoku-to was 63 and 74 microg/ml, respectively. In the crude drug ingredients tested, Scutellaria baicalensis G. and Coptis japonica M. which are the main components of san'o-shasin-to and oren-gedoku-to, showed the most powerful antitrypanosomal activity. The MEC and EC50 value of these crude drug ingredients were 30 and 60 microg/ml, and 20 and 36 microg/ml.