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Eye movements induced by head rotation were studied in 6 patients in acute coma, 4 patients in a persistent vegetative state, and 6 healthy, alert control subjects. Results from control subjects suggest that the oculocephalic response in the supine position is principally a vestibulo-ocular reflex. A position-step rotation of the head produced an initial oppositely directed eye movement, followed by a drift of the eyes back toward midline with a negative exponential time course. The time constant of this drift was greater than or equal to 10 seconds in control subjects but less than or equal to 1.5 seconds in unconscious patients and less than or equal to 0.5 seconds in vegetative patients. The rapid drift back of the eyes in unresponsive patients implies dysfunction of reticular and, possibly, cerebellar connections; the rate of this drift may indicate the severity and extent of brain injury. Sinusoidal head rotation produced slow and quick phases of nystagmus in normal subjects. Quick phases were absent in patients in acute coma; although present in vegetative patients, the quick phases did not keep the eyes close to primary position, as was the case in control subjects.