A corticotropic hypothalamic area whose lesion led to reduced pituitary-adrenal cortical activity in the pigeon was investigated by means of electrical stimulation with chronically implanted deep electrodes. 300 µA current intensity, 1 msec pulse duration, 60 cps frequency in alternating 10 sec (+) and 10 sec (–) trains over a period of 10 min, as parameters of stimulus, were found to be effective when delivered into the posterior medial lateral hypothalamic region. The plasma corticosterone level sharply increased immediately after the stimulation period and then decreased slowly to the prestimulatory value, 16 min later. Stimulation of other hypothalamic areas with the same parameters did not elicit any change in plasma corticosterone level. Behaviorally, no signs became apparent during the period of stimulati