Abstract: Apparatus is disclosed for detecting wheel slip of a driven wheel with respect to a surface. A magnet is fastened to the wheel and a sensor coil is fixedly mounted adjacent the path of rotation of the magnet. The sensor generates one electrical pulse each time the associated magnet rotates past it. Thus, the time of rotation of the wheel corresponds to the time interval between the pulses provided by the coil. The rotation time of the driven wheel is compared against the rotation time of a similarly equipped free rolling wheel to detect wheel slip. A wheel slip indication is given if the difference in wheel rotation times is greater than a selected limit. Acceleration of the wheels may interfere with the wheel slip detection, because the rotation times of the driven and free rolling wheels are not measured at precisely the same time.