Because of the usually low spontaneous activity of oxytocin producing cells, the effect of low frequency (6 Hz) electrical stimulation of the pituitary stalk in vivo upon plasma oxytocin concentration, uterine contractions and intramammary pressure was studied. 30 min of stimulation increased plasma oxytocin concentration. The same type of stimulation elicited both uterine contractions in early post portion rats and milk ejection in the lactating rat, but the latter phenomenon was not considered to mimic physiological events as contrasted with the former. It was concluded that in contrast to previous data, below 10 Hz stimulation of the pituitary stalk in vivo is also effective in producing hormone release and, furthermore, that it may have physiological consequences.