The effects of ether and of photic and acoustic stimulation on adrenocortical responses were studied in normal rats and in animals with lesions in the ventral mesencephalic tegmentum and mammillary peduncles and with posterior deafferentation of the hypothalamus. The mesencephalic lesions had no effect on adrenocortical responses. Rats with mammillary peduncular lesions and with posterior deafferentation exhibited only a slightly reduced response to ether stress; however, the responses to photic and acoustic stimuli were inhibited very considerably, when compared to intact animals. The present data indicate that photic and acoustic stimuli, which activate adrenocortical responses, depend upon the intactness of afferent ascending pathways, which include the mammillary peduncle and the medial forebrain bundle.