Mitotic rhythms were investigated in the chick corneal epithelium under various lighting regimens. Day‐old chicks were subjected to LD 14:10 (14 hr‐light: 10 hr‐darkness) for 2 weeks and the number of mitotic cells were counted in the central and peripheral regions of the cornea. The mitotic activity was high in darkness and low in light, and higher activity in the central region than in the peripheral region was observed. Anticipatory sharp rise in mitotic activity was observed just after light off. When chicks were reared in LD 12:12 (light on 06:00–18:00) and in inverted LD 12:12 (light on 18:00–06:00), the phase of the rhythm in normal LD 12:12 was different by 180° from that in inverted LD 12:12. When chicks were transferred to continuous light or continuous darkness after 2 weeks in LD 14:10, the mitotic rhythm disappeared in continuous light, but it continued in continuous darkness, suggesting a circadian nature of the rhythm. Two‐day old chicks, which were given only one LD cycle, also showed a distinct mitotic rhythm. Chicks kept in continuous light for 13 days could not recover the mitotic rhythm when they were transferred to continuous darkness.