Cerebral electrostimulation of subconvulsive intensity causes a pronounced increase in the concentration of adrenaline-like substances in the blood (Weil-Malherbe and Bone, 1952b). This effect is presumed to be due to a central action of the current, since these investigators were unable to demonstrate any rise when both electrodes were placed on the same side of the head. The current which was used in these experiments consisted of brief rectangular impulses with a repetition rate of 100 pulses per second (Montagu, 1953). Recently, while experimenting with shorter pulses at correspondingly higher repetition rates, the author observed that the motor response diminished as the frequency was raised, the peak and average current levels remaining constant. This effect, which appeared to be due to the progressive abbreviation of the pulses to the point at which they ceased to be effective motor stimuli, suggested that these conditions might be advantageous in electrostimulation therapy, provided that the autonomic effects were not equally impaired. Firstly, however, it was necessary to determine whether the diminution in the motor effects at the higher frequencies was part of a generalized reduction in the efficiency of cerebral stimulation or whether there was a differential response. Accordingly, with the assistance of Dr. Weil-Malherbe, the blood adrenaline level has been studied in relation to the different conditions of stimulation. The results of this investigation are contained in the present report.