Electrical stimulation of the hypothalamus in 181 mature female Holtzman rats with monopolar electrodes, using 1.0 mA intensity square wave pulses of 5 msec duration and 50 cps, showed that plasma growth hormone rises occurred only when the stimulation sites were located in the ventromedial hypothalamic nuclei, their border zones, and the median eminence. Equivocal growth hormone changes were observed in several anterior and posterior hypothalamic areas and are attributed to a spread of current via intrahypothalamic fiber systems. The results suggest that the hypothalamic control of growth hormone secretion is localized in the immediate vicinity of the ventromedial nuclei.