Through recent advances in molecular biology, especially biotechnology, regulatory agencies are faced with evaluating a range of biological agents for potential risks they pose to human health and the environment. Although biological risks are of relatively recent concern, this has not been the case for chemicals. Over the past several years, the Environmental Protection Agency (EPA) has developed methodologies for assessing health risks associated with chemical pollutants, especially chemical carcinogens. In anticipation of regulating biological agents, including genetically engineered microorganisms, the Agency must stimulate the generation of a solid scientific basis in order to adapt its present, chemically based risk assessment approaches to biological agents. Assessing biological risk poses unique problems owing to the diversity (hormones, enzymes, bacteria, fungi, viruses, plasmids) and the ability of live molecules to replicate, transform, transduce, and infect.