The recent identification and differential localization in brain of three binding sites for corticotropin-releasing factor (CRF)-like peptides (CRF1 and CRF2 receptors as well as CRF-binding protein) suggest the existence of functionally distinct neurobiological systems which mediate CRF activation. For instance, evidence from receptor knockdown and pharmacological studies suggest involvement of the CRF1 receptor in anxiogenic-like behavior and the CRF-binding protein in learning and memory processes. The present studies examined the potential functional significance of the CRF2 receptor in relation to the CRF1 receptor using two animal models of anxiety and endocrine reactivity to a stressor. CRF1 and CRF2 receptor knockdown was achieved and confirmed autoradiographically within brain regions relevant to behavioral reactivity to stressors by chronic, central administration of antisense oligonucleotides. CRF1 but not CRF2, know down produced a significant anxiolytic-like effect in the Defensive Withdrawal relative to vehicle-treated and two missense oligonucleotide negative control groups. In contrast, neither antisense treatment altered endocrine or behavioral reactivity to a swim stressor. Thus, the present data support the reported role of CRF1 receptors in the mediation of anxiogenic-like behavior and suggest a functionally distinct for role for CRF2 receptors in brain.