The purpose of the NIMH Toxicological Evaluation of Novel Ligands Program is to accelerate the discovery, development, and application of novel ligands for imaging in humans. The program will also facilitate the discovery and development of novel psychoactive agents for clinical research and as potential therapeutic agents for the treatment of mental disorders. This initiative will provide a critical resource that complements NIMH?s existing Psychoactive Drug Screening Program for pharmacological characterization of novel compounds in binding assays for receptors, channels, and transporters in the central nervous system and in biochemical assays to assess functional activity. The Toxicological Evaluation of Novel Ligands Program will also complement the initiative to accelerate the Development of Novel PET and SPECT Ligands for Brain Imaging for use in human studies. Efforts of these activities will be coordinated to establish a pipeline for the rapid and cost-effective development of novel ligands for clinical studies of mental disorders.