In sheep, 26 brain areas of 62 investigated contained corticotropin releasing factor (CRF)-like immunoreactivity in concentrations higher than 0.5 ng CRF/mg protein. Most of the CRF in the brain was in the hypothalamus. The highest level of CRF in the sheep brain was in the median eminence, almost two orders of magnitude higher than anywhere else. All of the hypothalamic nuclei had measureable amounts of CRF. A number of extrahypothalamic regions such as amygdala, hippocampus, claustrum, cingulate cortex, habenula and certain lower brainstem nuclei had CRF but generally in very low concentrations.