Frequency control in the Cosmotron is based on a signal derived from a pickup loop in the magnet gap. This signal is integrated electronically and is then distorted in a nonlinear network to yield a control voltage for the saturable-core oscillator. System constants are chosen such that the oscillator frequency has, at all times, the value associated with the instantaneous Cosmotron magnetic field. Dynamic frequency is measured by counting cycles for one millisecond at any desired time during the cycle. Tests on the present system indicate that it is adequate, but that several simplifications are possible.