gamma-Mangostin isolated from the fruit of Garcinia cambogia is an HIV protease inhibitor. gamma-Mangostin is cytotoxic to HL-60, SMMC-7721, A549, MCF-7, and SW480 cancer cells and BEAS-2B non-cancerous pulmonary epithelial cells in vitro (IC50s = 7.39, 6.57, 10.07, 5.33, 8.4, and 7.43 μM, respectively).