Xanthohumol (XN), the chalcone from beer hops has several biological activities. XN has been shown to induce apoptosis in cancer cells and also has been reported to be involved in lipid metabolism. Based on these studies and our previous work with natural compounds, we hypothesized that XN and its isomeric flavanone, isoxanthohumol (IXN), would induce apoptosis in adipocytes through the mitochondrial pathway and would inhibit maturation of preadipocytes. Adipocytes were treated with various concentrations of XN or IXN. In mature adipocytes both XN and IXN decreased viability, increased apoptosis and increased ROS production, XN being more effective. Furthermore, the antioxidants ascorbic acid and 2-mercaptoethanol prevented XN and IXN-induced ROS generation and apoptosis. Immunoblotting analysis showed an increase in the levels of cytoplasmic cytochrome c and cleaved poly (ADP-ribose) polymerase (PARP) by XN and IXN. Concomitantly, we observed activation of the effectors caspase-3/7. In maturing preadipocytes both XN and IXN were effective in reducing lipid content, XN being more potent. Moreover, the major adipocyte marker proteins such as PPARγ, C/EBPα, and aP2 decreased after treatment with XN during the maturation period and that of DGAT1 decreased after treatment with XN and IXN. Taken together, our data indicate that both XN and IXN inhibit differentiation of preadipocytes, and induce apoptosis in mature adipocytes, but XN is more potent. © 2007 Springer Science+Business Media, LLC.