Corticotropin-releasing factor (CRF) and interleukin-1 (IL-1) are two major components of the brain-endocrine-immune response to stress. We identified, characterized, and localized CRF and IL-1 receptors in brain, pituitary, and spleen using 125I-CRF and 125I-IL-1 alpha, respectively. 125I-CRF binding had comparable kinetic (KD:200-400 pM) and pharmacological characteristics in brain, pituitary, and spleen. In studies using cross-linking techniques, 125I-CRF was incorporated in rat pituitary and mouse spleen homogenates into a complex of Mr = 75,000 and in rat brain, into a complex of Mr = 58,000. The differences observed in the molecular weights between the pituitary and splenic vs. brain CRF receptors were evident across a variety of species and appeared to be due to differential glycosylation of the receptor proteins. In autoradiographic studies, CRF receptors were localized in highest densities in anterior pituitary and in brain regions involved in cognitive function, in limbic areas involved in emotion, and in brain areas regulating autonomic and other stress-related responses. In spleen, CRF binding sites were localized in the macrophage-rich red pulp and marginal zone surrounding the white pulp regions. High affinity 125I-IL-1 alpha binding sites were identified in pituitary membranes with kinetic and pharmacological characteristics comparable to the well-characterized IL-1 receptors in the EL-4 6.1 mouse thymoma cell line. Preliminary studies have identified IL-1 receptors in discrete regions of mouse brain. These data further substantiate the physiological role of CRF and IL-1 in modulating the brain-endocrine-immune axis.