In vitro assays involving primary cells are used routinely to evaluate organ-specific toxic effects, for instance, the use of primary hepatocytes to evaluate hepatotoxicity. A major drawback of an in vitro system is the lack of multiple organ interactions as observed in a whole organism. A novel cell culture system, the integrated discrete multiorgan cell culture system (IdMOC), is described here. The IdMOC is based on the "wells within a well" concept, consisting of a cell culture plate with larger, containing wells, within each of which are multiple smaller wells. Cells from multiple organs can be cultured initially in the small wells (one organ per well, each in its specialized medium). On the day of toxicity testing, a volume of drug-containing medium is added to the containing well to flood all inner wells, thereby interconnecting all the small wells. After testing, the overlying medium is removed and each cell type is evaluated for toxicity using appropriate endpoints. We report here the application of IdMOC in the evaluation of the cytotoxicity of tamoxifen, an anticancer agent with known human toxicity, on primary cells from multiple human organs: liver (hepatocytes), kidney (kidney cortical cells), lung (small airway epithelial cells), central nervous system (astrocytes), blood vessels (aortic endothelial cells) as well as the MCF-7 human breast adenocarcinoma cells. IdMOC produced results that can be used for the quantitative evaluation of its anticancer effects (i.e., cytotoxicity towards MCF-7 cells) versus its toxicity toward normal organs (i.e., liver, kidney, lung, CNS, blood vessels).