We examined the antimetastatic effect of acteoside, a phenylethanoid glycoside widely distributed in the plant kingdom, on lung metastasis using a mouse model injected with B16 melanoma cells intravenously. Male C57BL/6 mice were injected intravenously with 2 x 10(5) of B16 melanoma cells, while acteoside at a dose of 50 mg/kg was administered intraperitoneally every other day from 13 d before B16 melanoma cell injection until all mice had succumbed to the metastatic tumor burden in the lung. Administration of acteoside prolonged survival time significantly and the average survival time was 63.3 +/- 3.4d compared with 52.1 +/- 2.5d in control mice. This result suggests that acteoside showed suppressive effect on lung metastasis of B16 melanoma cells.