The distribution of Cholecystokinin (CCK-8)-like immunoreactivity was mapped in the brain of the little brown bat, Myotis lucifugus, at three different and discrete levels of physiological activity: euthermic, hypothermic, and hibernating. Immunoreactive perikarya were present in the cerebral cortex, hippocampal formation, several nuclei of the olfactory and limbic systems, the ventral lateral geniculate nucleus, suprachiasmatic nucleus, medial geniculate nucleus, and caudate-putamen. Immunoreactive fibers were present in plexuses throughout the brain and in three major projection pathways: the medial forebrain bundle, the mammillary peduncle, and dorsal longitudinal fasciculus. Our data suggest two possible loci for CCK regulation of feeding behavior: a hypothalamic locus in the dorsomedial nucleus and a brainstem locus in the nucleus tractus solitarius.