Six postmenopausal women with frequent attacks of flushing were studied by measuring plasma luteinizing hormone (LH), follicle stimulating hormone (FSH), prolactin and noradrenaline concentrations at regular and frequent intervals and at the time of each of 82 flushes. The hormone measurements were made on a control day and on the second day during infusion of either naloxone (22 micrograms/min) or saline. The perception of a flush was associated with a significant increase of plasma LH concentrations. There were no significant changes in plasma FSH, prolactin or noradrenaline concentrations. Naloxone infusion resulted in a highly significant reduction in the frequency of flushes and in the number of LH pulses. We conclude that flushing and its neuro-endocrine correlates are related to activation of opiate receptors. Naloxone may provide the basis for a non-steroidal treatment of climacteric flushing attacks.