Recent scientific investigations have shown that many chemicals used in plastics, pharmaceuticals, )esticides, cosmetics, food additives, etc. are endocrine disruptors (EDs). EDs interfere in various ways with hormonal activity to have significant adverse effects on many physiological processes at very low (picomolar to nanomolar) concentrations, especially on fetal or developing mammals. The prevalence and actions of EDs in our environment warrants the development of highly specific, sensitive, reliable, rapid, and cost-effective detection. Consequently, various governmental bodies (EPA, FDA, and ICCVAM) and proactive corporations explicitly desire an in vitro robotic assay for EA, but no such assay is commercially available, much less validated. CertiChem (CCi) has just successfully completed a Phase I SBIR project to demonstrate that it is feasible to develop a robotic assay for EA using MCF-7 cell proliferation. In this Phase II application, CCi proposes to improve and extensively validate this assay so that it can be fully commercialized in Phase III. CCi also proposes to examine the relationship between theoretical predictions of EA for a set of antioxidants used in foodstuffs and plastics and the actual EA as measured by this robotic cell proliferation assay. Validation of our robotic screening assay for EA should be commercially important because of the large number of chemicals (>10,000) - much less chemical mixtures -that should be screened for EA by profit, non-profit, or governmental entities. Data from our robotic assay will also be of commercial importance because it will enable us to design proprietary formulations of additives that lack EA for foodstuffs and plastics.