Unusual blink reflex with four components in a patient with periodic ataxia. Characteristic findings in blink reflex are reported in a 55-year-old female with periodic ataxia. The blink reflexes on the side ipsilateral to the stimulation consisted of four components with latencies of 11, 21, 35 and 47 ms, instead of the usual two components seen in normal subjects. On the contralateral side, the last three components were also present. The second component was different from the normal R2 response in that its latency was shorter than normal and it did not habituate by stimulation at a rate of 10 Hz. In addition, it was more affected by diazepam than the third or fourth components. It is considered that R2 may have consisted of three components and that a shorter latency of the second component could be explained by facilitation. 