For nearly two decades, the National Institute on Drug Abuse has provided the scientific community working on problems of drug abuse with authentic, standardized supplies of controlled research drugs and chemicals. These include known hallucinogens, heroin, amphetamines, cannabinoids, and many other drugs essential for both clinical and laboratory research studies. Recently, the isolation of Leu5-enkephalin, Met5-enkephalin, and other opioid peptides has generated an explosive interest in this research area. Following these discoveries, evidence was presented for the existence of multiple populations of receptors. These exciting discoveries attracted a host of scientists such as medicinal chemists, pharmacologists, biochemists, clinicians, behavioral scientists, molecular biophysicists, and neuroendocrinologists, to conduct research in this area. This active research area has generated the need for several pure opioid peptides in large quantities for a number of preclinical and clinical studies supported by NIDA--receptor-binding studies, evaluation of addiction and analgetic potential, pharmacokinetics studies, and conformational studies by C.D.; N.M.R.; X-ray, laser-Raman, and FT-IR, etc. The opioid peptides and their respective intermediates compounds are expensive and purity is not always sufficiently, established. In order to provide pure crystalline opioid peptides to researchers for NIDA supported studies, NIDA has awarded two contracts to synthesize, maintain an inventory of and supply various peptides and their intermediates. One contractor synthesizes these peptides by the solid phase and the other by the conventional (solution phase) methods. The purity and authenticity of these peptides are further needed to be determined and monitored. Therefore, through this contract NIDA intends to establish, monitor and maintain the purity of peptides for the NIDA supported research.