The recent identification of ovine corticotropin releasing factor (CRF), a 41-amino acid peptide, provides a potential new approach to evaluate disorders of the hypothalamic-pituitary-adrenal axis. We report here the effects of this new factor in the pituitary stalk-sectioned cynomolgus macaque. Given as an intravenous bolus, CRF stimulated cortisol secretion with an ED50 between 0.1 and 1 microgram/kg body weight. The peak cortisol response occurred after 15--30 min at low doses (0.5--1 microgram/kg) and after 45--90 min at higher doses (2--40 microgram/kg). This factor also stimulated the release of growth hormone and prolactin, but had no effect on TSH or LH secretion.