The purpose of this study is to characterize an ocular permeability of FITC-dextran, as a model of peptide drug, and to evaluate the effects of absorption promoters on the ocular permeability of FITC-dextran. The in vitro penetrations of FITC-dextrans (average molecular weight 4400 and 9400: FD-4 and FD-10) were measured across the isolated corneal and conjunctival membranes of albino rabbits using a two-chamber glass diffusion cell. The corneal permeabilities of FD-4 and FD-10 were much lower than the conjunctival permeabilities. Scraping of corneal epithelium extremely increased the corneal permeabilities. The penetration parameters were estimated according to Fick's equation. Absorption promoters such as EDTA, taurocholic acid, benzalkonium chloride and saponin significantly increased corneal permeabilities of FD-4 and FD-10. Saponin showed the highest promoting activity. Conjunctival permeabilities of FD-4 and FD-10 were also enhanced by absorption promoters although the improvements of conjunctival permeabilities by absorption promoters were smaller than those of corneal permeabilities. Ratios of corneal to conjunctival permeabilities were enhanced by absorption promoters. These results indicate that an ocular delivery of instilled hydrophilic macromolecule is markedly low and a selective use of absorption promoter can improve the extent and pathway of its ocular absorption.