There is described the operation and calibration of an electronic stimulator which supplies a unidirectional, rectangular current pulse of variable frequency, amplitude, and pulse length (length of the conducting portion of the cycle). Each of these three variables is independent of changes in the other two, and the amplitude is virtually independent of variations in the resistances of individual subjects. The range of frequencies extends from one cycle in several minutes to 20,000 cycles per second. With the maximum amplitude of 2 milliamperes the resistance of the subject may be as great as 200,000 ohms; smaller amplitudes or a slight modification of the circuit permits the allowable resistance to be increased. The pulse length may be varied from a minimum of110of the cycle to any desired value.