Studies of the dynamic characteristics of horizontal saccadic eye motion give velocity, acceleration, and timing information. Average time differences between the motion of the eyes on left and right gaze, termed “differential delays,” are statistical measures of the average differences of right-going and left-going velocity waveforms, and can be determined to within 0.5 msec. These relative time measurements give information that is not necessarily apparent from the velocity or acceleration data, and provide a sensitive measure of early oculomotor dysfunction. Patients with internuclear ophthalmoplegia have been shown to give characteristic abnormal values, and two such patients are described in detail to illustrate how these measurements may be used both to help in diagnosis and to characterize the presumed lesions.