A theoretical study of dynamic processes within the cyclotron leading to pulsing of the ion beam is presented. The main factors determining the shape and duration of natural pulsing of the beams were studied experimentally. It was found that the form and duration of cyclotron natural pulses depend on special working conditions, e.g., compensatory coils of the median plane and azimuthal shims, and are not uniquely determined by parameters such as dee gap width, r-f voltage, and resonant frequency. Shorter pulses can be obtained with higher r-f voltages, contrary to expectation. The implications of the results are discussed. (D.L.C.)