The orbicularis oculi reflex elicited by electrical stimulation of the supraorbital nerve was studied in 39 cases with vascular lesions of the brainstem (four mesencephalic, 14 pontine, 13 medullary and eight multilevel), six cases following severe anoxic episodes and two cases of traumatic brainstem lesions. The early reflex (normal latency: 10.6 ± 2.5 msec) was delayed in 20 out of 22 cases with pontine or multilevel brainstem strokes and in all the eight cases of anoxic or traumatic brainstem lesions. The direct (31 ± 10 msec) and consensual (32 ± 11 msec) late reflexes, analogously to the pupillary light reflex, were useful in distinguishing afferent, efferent, and other blocks. In all the seven comatose patients, the late reflex was virtually absent. However, a relatively normal early reflex was present in four of these. The findings of this study indicate that the brainstem conduction altered by vascular and anoxic lesions can be measured simply and objectively by the orbicularis oculi reflex. A delay of the early reflex is relatively specific to pontine lesions. The late reflex is not only altered by brainstem lesions but is also totally depressed in coma, presumably reflecting diffuse suppression in multisynaptic reticular system.