The purpose of the present study was to examine in the bed nucleus of the stria terminalis (BST) of the rat brain the morphological characteristics of interactions between corticotropin-releasing factor (CRF)-producing neuron populations and serotonin (5-HT) axons. A double-label immunocytochemical, light microscopic technique was used to demonstrate axosomatic and axodendritic interactions between 5-HT axons and CRF neurons in the BST. Both the dorsolateral and ventrolateral subpopulations of CRF neurons were targets for the 5-HT afferents. Projections of monoamine neurons to the BST and the CRF neurons that are in the BST are implicated as being major contributors to the neurochemically mediated central regulation of the stress response.