During the last 25 years we have attended to the formation of new and important fields in the neuroscience domain. Due to the study of neuropeptides. Virtually, the neuropeptides represent a new class of chemical transmitters, many of wich could act as endocrine, amacrine or paracrine hormones. In addition, the neuropeptides were also found to influence other higher functions, including cognition and memory. The biochemical diversity in neurons has revealed the coexistence, in the same neurons, of classical small transmitters with neuropeptides. This finding offers new and promisory perspectives in the synaptic transmission. At this time, the largest group in the neuropeptide families could be that of the opioid peptides. Endorphins could be the best studied and characterized group, because of their implications in the narcotic mechanisms of action and treatment of pain. In this work, we recalled briefly the historical background of the discovery of enkephalins and we reviewed the biochemical characteristics implicated in the opioid peptide metabolism: the biosynthesis, release, catabolism and receptor binding. We also analyzed updated data concerning the opioid peptide physiology. The accumulated knowledge of two decades of study of biochemistry, pharmacology, physiology and the distribution of the opioid peptides, together with the molecular biology technics and the modern clinical diagnostic technology, such as the positron emission tomography and the nuclear magnetic resonance, promise new perspectives and possibilities of therapeutical intervention.
