Awareness of environmental contamination and possible health consequences have grown significantly and resulted in increased efforts to monitor and understand the effects of individual compounds. However, this research does not reflect the reality that we are routinely exposed to a variety of environmental contaminants, ranging from metals to industrial compounds. Many environmental chemicals influence the same endpoint, namely the selenium-dependent glutathione peroxidase (Se-GPx), although the chemicals have different chemical structures and mechanisms of toxicity. This proposal addresses the issue of chemical mixtures and is supported by recent papers suggesting a connection between selenium and/or Se-GPx and chemical carcinogenesis. This research will investigate the effects of combinations of environmental chemicals on Se-GPx by employing cell culture and in vivo experiments.