Throughout my career as a toxicologist, I have observed that toxicology studies in drug development, are sometimes considered as being only a box-checking exercise on the path to the clinical trial. While this can be so in a limited respect, I think it is underappreciated that definitive toxicology studies, and related studies, serve a highly critical purpose. That is, they help identify potential safety issues and target organs in humans, to identify translational markers of potential toxicity in later human trials and most immediately and importantly they can provide high quality and reliable data on which to base the safe starting dose in humans. Without these definitive studies, or with poorly conducted or interpreted studies, the risk to trial participants and to eventual patients, is simply too high. So, the data from these studies, and particularly the NOAEL information is essential for the safe and effective development of new drugs.