Abstract: A non-invasive apparatus for monitoring physiological responses for detecting the presence of drug impairment. The oculomotor and pupillary system is monitored and evaluated to detect the ingestion of drugs and the impairing effect or influence thereof. The horizontal, vertical, oblique and torsional eye movement, eye lid blink activity as well as the size and reactivity of the pupil are the primary data sources. An enclosed chamber surrounds each of the eyes of the subject, and thereby precludes the admission of ambient light. Within each chamber are disposed point sources of infrared radiation specifically oriented with respect to the subject's eye. An infrared sensitive video camera is positioned to minimize the effect of cosine compression within each chamber relative to the subject and is positioned with respect to the infrared radiation sources in order to provide maximum contrast between the pupil and iris of the eye.