Twenty-two patients and 7 normal subjects at the Burdenko Institute of Neurosurgery, Moscow, have taken part in an investigation in which the direct light reflex to a brief flash, and the high-frequency microtremor of the eyes, have been recorded. The direct pupil reflex recordings obtained with a flash of 20 msec duration and 100 lux intensity at the plane of the pupil were registered from the right eye of each patient. Ocular microtremor recordings were obtained simultaneously from both eyes of 20 of the patients. A set of criteria of abnormality of ocular microtremor, as judged by visual examination of the records, is proposed by the authors. Abnormality of the pupil reflex is assessed in terms of the amplitude, latent period, and time course of the contraction and relaxation phases of the reflex. A strong correlation has been found between the occurrence of an abnormal ocular tremor record and an abnormal pupil reflex. On the basis of this correlation, the authors propose that ocular tremor recordings may be used in diagnosis as sensitive indicators of brain-stem dysfunction.