Identification of novel new molecules which hold the greatest promise of safe and effective therapies remains a continuous challenge to the pharmaceutical industry. This has led the industry to implement strategies for identification of the most promising candidates during the discovery phase and for their safe and expeditious advancement through development. Testing for potential liable properties in the discovery phase has included the evaluation of major areas of pharmaceutics that have led to failure such as its physical and pharmaceutical properties, drug metabolism and pharmacokinetic characteristics, various safety endpoints including pre-development safety pharmacology, general toxicology and genetic toxicology and interrogation of counter-screen data to identify off-target affinities (i.e., receptors, ion channels, transporters, kinases, etc.) that pose a concern. Amongst the many important areas of concern is the potential for toxicities of the major organ systems. To mitigate this concern, a strategy pursued is to identify the prominent toxicological properties of the candidate prior to its recommendation for development. The results of these studies in discovery allow exclusion of the candidate before the expenditure of resources and time typical of development. In addition, the discovery phase toxicology studies serve to address key questions that may have arisen from the study of another molecule, the phenotypic profile from pre-clinical models where the therapeutic target has been genetically modified or concerns that have been raised as a result of other investigations. Importantly, the results of the exploratory drug safety studies will be used by the sponsor to judge the potential risks associated with continued pursuit of a potential development candidate. In many ways, pre-clinical toxicological investigations in discovery serve the important objective of identifying the most promising candidates to progress into development and onto registration.