A significant challenge facing the cancer research community is the identification of proteins that present therapeutic opportunities for the specific elimination of cancer cells. This application presents a rational approach to the discovery of novel anti-cancer targets that is based upon the genetic principle of synthetic lethality. The goal is to identify mutations which are tolerated on their own but which are incompatible with alterations in oncogenes and tumor suppressors that are commonly if not universally altered in cancer cells. Such a search is, at a minimum, technically daunting in mammals. However, the availability of facile genetic tools and fully sequenced genomes make model organisms an attractive alterative. It is well established that Drosophila is a convenient model in which to examine oncogene and tumor suppressor pathways. We have recently demonstrated that RNA interference can be used to ablate gene expression in cultured Drosophila cells. In this exploratory application, we propose to take advantage of the Drosophila unigene set to create an array of cell strains in which each gene in the set is disrupted individually. The viability of cells containing each disruption will be evaluated in the absence and in the presence of either activated ras or Rb-loss. Cell strains that show apoptosis only in the presence of the cancer mutation will identify synthetically lethal interactions. The development of this technology will allow not only allow a search for anti-cancer targets but will also undoubtedly find application to a broad range of biological problems.