The possible role of different kind of photoreceptors in synchronization of circadianlocomotoractivity in cockroaches is presently still contradictory. We try to clarify the part played by the compound eyes and the ocelli with lesion and black‐varnishing experiments. The locomotor activity of isolated animals is automatically recorded in ring‐shaped cages equiped with infra‐red beams. Circadian rhythms are detected by using the Whittaker and Robinson periodogram.