Thevetoside (TS) is one of the cardiac glycosides. A study of antitumor activity was carried out in 6 types of murine tumors in vivo, such as the ascitic tumors H22, EAC, P388, and solid tumors S180, U14, Lewis lung carcinoma, which were treated with i.p. TS 1.5 mg.kg-1.d-1 alone or in combination with chlormethine (Chl) 0.3, 0.5, or 1.0 mg.kg-1.d-1. TS only showed a remarkable inhibition on the growth of 3 types of solid tumors with inhibition rates of 48.7%-56.7%. The effect of the combination therapy was much pronounced than that of independent administration. The life span under combined therapy was increased 82.4% to > 122.1%. For solid tumors, the combined administration gave inhibition rates of 65.6%-72.5%.