Previous experiments from this laboratory using the hypothalamic island have demonstrated that the adrenocortical discharge following sciatic nerve stimulation is mediated by neural pathways only. With the purpose of identifying the neural structures involved, this response was studied in rats with bilateral lesions in the medial forebrain bundle (MFB), mammillary peduncle (MP), fasciculus longitudinalis dorsalis (FLD), mid-brain reticular formation (MRF) and the medial geniculate body (GM). Lesions in the MFB, MP and MRF have inhibited the adrenocortical response following sciatic nerve stimulation. These and other data indicate that the above structures are involved in the mediation of this response and that the afferent pathway enters the mediobasal hypothalamus anteriorly.