The retinal ciliary margin is particularly relevant for the correct generation and regeneration of vertebrate retinae, since pluripotent stem cells are located there throughout development, and--at least in some species--even until adult stages. Our aim was to identify factors (genes) which are involved in processes of proliferation and differentiation in the developing chicken retina. Reverse transcription-polymerase chain reaction differential display was used to identify genes that were differentially expressed in chick central and peripheral embryonic retina. Candidate genes analyzed through sequencing and database searches were confirmed by Northern blot analysis and histochemistry. A series of differentially expressed genes were detected, including a neuronal cell adhesion molecule, an esterase, and homeobox gene products. One of the sequenced products was identified as subunit I of cytochrome-c oxidase (COX-1), an enzyme which is central to energy metabolism and particularly relevant for developing nervous systems. Northern blot analysis confirmed its up-regulation in the chick peripheral retina, being maximal at embryonic day 7. In the retinal pigmented epithelium its expression is lower than in the retinal periphery but higher than in central retina. COX histochemistry revealed distinct laminar patterns in central retina, but also an elevated level of activity in the peripheral retina throughout development. These data not only show that the developing ciliary margin of the chick retina has high energy requirements, but also indicate that COX-1 could play essential roles in developing cells and in stem cells of the eye periphery.