Risk assessment (RA) can be defined as a systematic iterative process that helps to characterize potential adverse health effects in humans following exposure to chemical substances in their home or work environment. The risk assessor is often interested in first identifying the hazardous substance and then describing and quantifying the risk based on evidence from sound human and/or animal toxicology studies. As often stated, ‘‘it’s the dose that makes the poison,’’ the primary focus in any chemical RA exercise is to be able to provide a quantitative relationship between the dose and adverse health effect and then be able to determine at what exposure level the human population is least likely to be at risk of experiencing adverse health effects from the chemical in question. Ultimately, the risk assessor is focused on arriving at the dose metric or some expression of the toxicologically relevant dose in the target organ. The simultaneous growth in microcomputer capability and software, the mechanistic data from advances in molecular biology, and the biologically based dose-response models in the last decade have allowed the risk assessor to better quantify the human health risk associated with exposure to potentially hazardous chemicals. The reader should be aware that although there have been significant advances in the art and science of the process, there are still many hurdles to overcome in our attempt to reduce uncertainty in the RA process.