Using the unlabeled antibody peroxidase-antiperoxidase (PAP) technique at the light microscopic level the distribution of immunoreactive corticoliberin has been studied in the hypothalamus and hypophysis of the sterlet. Corticoliberin-containing cells have been revealed in the nucleus tuberalis and to lesser degree in the nucleus preopticus of the hypothalamus. The majority of labeled cells is located subependymally or between the ependymal cells. Some dendrites of corticoliberin-containing cells can be followed toward the ventricular lumen. Their axons project to the anterior neurohypophysis (proximal neurosecretory contact region) where they terminate in contact with the primary portal capillaries. Single terminals containing immunoreactive corticoliberin are seen in the roots of the posterior neurohypophysis on the border region between the neurohypophysis and the hypophysial pars intermedia, and sometimes in contact with the capillaries of the general circulation. The possible role of corticoliberin in the regulation of the function of glandular cells of both the pars distalis and pars intermedia is discussed.