The electrically and optically elicited orbicularis oculi reflex (OOR) and facial nerve latency were investigated in eight patients from three families. Each had autosomal dominant peroneal muscular atrophy. In a family with the dominantly inherited hypertrophic type markedly delayed latencies of the early reflex component of the OOR were found while the facial nerve had remained unaffected. These findings were interpreted as an indicator for supraorbital nerve involvement. In the other two investigated families of hypertrophic and neuronal type, a prolonged facial nerve latency was demonstrable. In these cases the latency of the optically evoked blink reflex was also delayed, while the latency of the early reflex component of the OOR was within normal limits or only slightly delayed. It is assumed that the different degree of cranial nerve involvement in these families is the expression of their genetically determined peculiarities.