The blink reflex may be evoked by auditory click or light stimulation, the latter being constantly present in all healthy subjects. The latency and amplitude of the light-stimulus-evoked blink response (L-BR) is influenced by the light intensity, distance between the light stimulus and the eye, attention, and background facilitation. The L-BR was abnormal in 75% of definite and 61% of probable multiple sclerosis (MS) patients. When abnormal, the L-BR was more commonly absent than delayed. Optic nerve lesions could be identified by the pattern of abnormalities in the L-BR in some patients. The L-BR has proved to be a sensitive detector of abnormalities in the visual connections and, in combination with the Vth nerve stimulation-evoked blink response, a valuable detector of brainstem lesions.