Vestibulocollic reflex(VCR) which stabilizes head position in space is essential for an adequate motor performance, and maintenance of balance and posture. The purpose of this study was to measure the VCR in brain stem lesion patients and to evaluate the usefulness of the VCR study in the evaluation of brain stem lesions. The VCR evoked by free fall of the head was measured by the electromyographic signal of the sternocleidomastoid muscles. Twenty normal and ten brain stem lesion subjects were studied by lying supine with the head cradled in a sling, and the VCR was evoked by an abrupt head drop while the sling was released. The electromyographic signal was recorded with surface electrodes from the sternocleidomastoid muscles. In normal subjects, the initial small burst with an onset latency at 20.61+/-3.25 msec was obtained followed by the later larger burst of sternoceidomastoid electromyographic response. But in the subjects with a brain stem lesion, the initial latency was delayed to 46.10+/-10.65 msec and the waveform was smaller and dispersed than that of the normal subjects. The VCR evoked by free fall of the head showed delayed latency and dispersed waveform in patients with a brain stem lesion. This method could be used for the evaluation of brain stem lesions.