Studies have been designed to investigate the effects of narcotic analgesics and opioid peptides (endorphins) on neuroendocrine function. The plasma levels of anterior pituitary hormones (adrenocorticotropin, thyrotropin, growth hormone, luteinizing hormone and prolactin will be measured by radioimmunoassay following acute and chronic administration of the opioids and during withdrawal from these compounds. Localization of the central sites and pathways of the opioids will be determined by the injection of microquantities of the drugs into specific brain sites, while using a neuroendocrine response for an endpoint, and by measuring their distribution in brain by radioimmunoassay and immunohistofluorescence.