The autoradiographic distribution of kappa opioid binding sites was evaluated in sections of monkey brain using the selective ligand [3H]dynorphin1-9. Kappa receptors were highly concentrated in the deep layers of the cerebral cortex, the substantia nigra, the hippocampus and the dentate gyrus. Lower levels were seen in the outer cortical layers, the caudate nucleus, the claustrum, parts of the amygdala and the cerebellum. These data are discussed in relation to the distribution in brain of the endogenous kappa-ligand.