This SBIR Phase II proposal elaborates on the success achieved during Phase I where IsoSciences was successful in developing synthetic methods for 1) The regioselective preparation of 2 and 4-methoxy-[13C,2H3] labeled estrogens and 2) The preparation of testosterone-[1,2,3-13C3]. The methodology developed in Phase I will be scaled up in Phase II such that IsoSciences, LLC will produce 100mg quantities of several stable-isotope labeled key steroid hormones including 2-, 3-, and 4-methoxyestrogens, estriol, testosterone, estrone, estradiol, and androstenedione and dehydroepiandrosterone. The selected compounds are believed to play critical roles in various cancers and thus have the potential to serve as cancer biomarkers. A significant stumbling block in the research area has been the lack of availability of stable isotope labeled standards for use in detecting and quantifying these key steroids. This Phase II contract will address that significant problem.