The spontaneous electrical activity of the neural lobe of the cat hypophysis has been recorded. We have observed two types of activity: (1) 0.5-1.0 mV in amplitude and 4–6 msec in duration, and (2) 0.03–0.07 mV in amplitude and 1–2 msec in duration. The discharge rates of both types of activity are affected by osmotic stimuli known to influence vasopressin release. Nevertheless, only the smaller potentials were studied because they were easier to obtain. The typical response to injections of hypertonic saline was an increase in the discharge rate characterized by two peaks in the frequency-time curve. This activity seems to correspond to the unit activity described by several authors for neurosecretory hypothalamic units. Hypotonic injections cause, in about 45% of the injections, a 50% decrease in the firing rate. Injections of isotonic saline did not alter the discharge rate by the neurohypophysis. We conclude that elements in the neural lobe of the pituitary are electrically excitable and respond to stimuli known to cause vasopressin re