Plasma γ-melanotropin was measured by a γ3MSH-specific radioimmunoassay before and after a single bolus intravenous infusion of ovine corticotropin releasing factor (oCRF; 0.1 ug/kg) in seven normal men. A significant increase of γ3MSH was observed 15 minutes post-oCRF infusion, which paralleled a similar increase in plasma cortisol. Bel filtration chromatography revealed that the observed increase was attributable to elevations of 9K and 4K forms of γ3MSH immunoreactivity. Affinity chromatography demonstrated that the majority of γ3MSH immunoreactivity in human plasma is glycosylated. As the smaller forms of γ3MSH are felt to have endocrine activity at the adrenal cortex, these changes may be physiologically relevant. © 1987.