AbstractScopadulcic acid B is a diterpenoid recently isolated fromScoparia dulcisL. This compound showed greater cytotoxicity against cell lines derived from tumour tissues with a 50% inhibitory concentration (IC50) of 0.068–0.076 μg/mL, compared with cell lines from normal tissues with an IC50of 0.097–0.245 μg/mL. Thein vivoantitumour activity of scopadulcic acid B was determined using mice inoculated with Ehrlich ascites tumour cells. Oral administration of the compound at doses of 25 or 100 mg/kg/day prolonged the median survival time of the animals. However, when administered intraperitoneally to mice at doses of 25, 50 or 100 mg/kg/day, scopadulcic acid B increased the survival rate by 12.5%, 12.5% and 25%, respectively, without weight change over the treatment p