We have measured corticotropin-releasing factor (CRF)-like immunoreactivity in the brain of 3 humans who had died of natural causes using a radioimmunoassay for human CRF. The peptide was widely and heterogeneously distributed and showed interspecies differences when compared with rat and rabbit. The highest concentrations were in hypothalamus, with substantial concentrations in cortex, and low or undetectable concentrations in several basal ganglia, cerebellum and hippocampus.