The naturally occurring peptide human beta-endorphin-(1-27) (h beta-EP-(1-27) has been shown to antagonize beta-endorphin (h beta-EP)-induced analgesia. We have evaluated the effects of the fragment on h beta-EP-induced growth hormone (GH) and prolactin (PRL) release. It inhibited beta-EP-induced GH release in a dose-related way but left beta-EP-induced PRL stimulation unchanged.