The total content and extent of processing of the γ3MSH and β-endorphin-containing N- and C-terminal domains of proopiomelanocortin were determined in the anterior and intermediate lobes of the pituitaries and in 11 regions of the brains of three Rhesus monkeys. Most immunoreactive γ3MSH and β-endorphin was located in the pituitary lobes, although significant amounts were also found in several brain regions. Sephadex column chromatography revealed that γ3MSH immunoreactivity was found primarily as 4K and 9K forms; no γ1MSH was detected. β-Endorphin immunoreactivity was found as β-endorphin, β-lipotropin, and as a 5K form which may represent β-endorphin extended N-terminally by part or all of β-MSH. In the anterior lobe of the pituitary, the predominant products were 9K γ3MSH and β-lipotropin; in the intermediate lobe, more processed forms (4K γ3MSH, β-endorphin and 5K β-endorphin) appeared to be preferentially stored. The pattern of processing in various brain regions was similar to that of the intermediate lobe of the pituitary. © 1988.