Here we investigate the kinetics of rat corneal epithelium at both single cell and tissue level by means of a BrdU-anti BrdU method. The results obtained have then been compared with those previously obtained by us in rat vocal cord epithelium. In this way two main aspects of BrdU incorporation can be indicated at both light and electron microscopy level. First, we report evidence of a new incorporation pattern corresponding to middle S phase, which is characterized by labelling distribution at the border between interchromatin and heterochromatin at ultrastructural level. Second, by comparing tissue incorporation in rats treated with BrdU at the beginning of light time and at the beginning of dark time, we show an increase of cell proliferation during the last hours of dark time and the first hours of light time. In this way, we demonstrate a different progression of circadian rhythms in peripheral regions of corneal epithelium in comparison with that previously observed in vocal cord epithelium.