Toxics regulation has long been constrained by limitations on our ability to determine the risk presented by any given chemical. Toxicogenomics is a cutting-edge technology that, according to its many adherents, promises low-cost, effective, quantified risk measurement. If these claims are true, toxicogenomic technology will produce a revolution in chemical risk assessment and regulation. The promise of toxicogenomics, however, may never be fulfilled because of the inherent complexity and heterogeneity of biological systems and the importance of environmental, rather than genetic, factors in toxic susceptibility. This Article describes the implications of toxicogenomics for environmental law, offering a critical perspective on the benefits and shortcomings of this technology. It concludes that toxicogenomics is unlikely to transcend the current chemical risk assessment paradigm, but that it is a valuable development nonetheless for enhancing our understanding of scientific uncertainty.