The crude chloroform extract of the bark of Alphitonia petriei (Rhamnaceae), collected from the Paluma Rainforest, north Queensland, Australia, exhibits cytotoxic activity against MDA-MB-231 (human mammary adenocarcinoma), MCF-7 (human mammary adenocarcinoma), and 5637 (human primary bladder carcinoma) cells.  The extract also shows antibacterial activity against Bacillus cereus.  Bioactivity-directed separation led to the isolation of 2-ketobetulonic acid and betulinic acid as the bioactive components.