Amooranin, 25-hydroxy-3-oxoolean-12-en-28-oic acid, is a triterpene acid isolated from Amoora rohituka stem bark. The cytotoxic effects of amooranin and its derivatives were studied. Amooranin and its methyl ester showed greater cytotoxicity against MCF-7 and HeLa cells derived from tumour tissues with a 50% inhibitory concentration (IC(50)) of 1.8-3.4 microg/mL, compared with Chang liver cells from normal tissue with an IC(50) of 6.2-6.4 microg/mL, but amooranin exhibited no activity on HEp-2 and L-929 cells. However, its monoacetate derivative showed no inhibitory activity at 1-10 microg/mL dose levels. Of the cytotoxic isolates, the methyl ester derivative was inactive in in vivo evaluations in the Ehrlich ascites tumour cells at 50 and 100 mg/kg/day, demonstrating T/C values of 106% and 114%, respectively.