Sensitive and specific radioimmunoassays for gamma- and beta-endorphin-like peptides (gamma E and beta E) were used to examine the distribution and relationship of these peptides in the pituitary and in microdissected nuclear brain areas of the male rat. In the pituitary, the highest amounts of gamma E and beta E were found in the neurointermediate region of the gland. On a molar basis, gamma E-like immunoreactivity was found to exist as a relatively constant proportion of beta E-like peptides throughout the pituitary. In the brain, while beta E-like peptides were detected in many brain areas, gamma E-like peptides were detected in only a limited number of sites. In most of these areas, the molar ratio of gamma E to beta E-like peptides closely approximated that found in the pituitary. However, in the ventromedial nucleus of the hypothalamus and nucleus accumbens a higher proportion of gamma E to beta E was measured. These results suggest preferential formation of gamma E or related peptides in certain areas of the brain may occur.