The frequency pulling and locking of intensity pulsations from continuously operating GaAs injection lasers have been studied by varying the frequency of the externally applied locking signal in the vicinity of the self-induced pulse rate or one of its harmonics. The ability of the laser pulse rate to follow a rapidly varying locking signal has led to the first realization of optical pulse position modulation with microwave repetition rates. Modulation rates attainable with this effect are expected to be as high as one-half the self-induced pulse rate. © 1969 The American Institute of Physics.