Opiate receptor distribution, determined by the autoradiographic localization of stereospecific [3H]diprenorphine binding sites, was examined in the telencephalon. Areas showing very dense or dense localization of receptors included parts of the presubiculum and amygdala, patchy areas in the caudate-putamen and accumbens, the subfornical organ, the interstriatal nucleus of the striae terminalis and the anterior olfactory nucleus, pars externa. Lower densities were found in other parts of the hippocampal formation, the deeper part of the cerebral cortex, the entopeduncular nucleus, globus pallidus, nucleus triangularis septi and nucleus paratenialis. The significance of these findings is discussed in terms of the biochemical and physiological actions of opiates.