Staining of the conjunctiva and cornea has been practiced for years as a diagnostic aid. Campbell and Boyd1 note that sodium fluorescein has been used by ophthalmologists for initial detection of breaks in the continuity of the epithelium of the cornea since 1882 (Pflüger, 1882; Straub, 1888). Berliner2 credits Knüsel and Von Miller for much of the original work in vital staining of the conjunctiva and cornea. More recently other authors have evaluated certain stains employed for specific uses; however, there is an obvious dearth of material concerning this subject. The importance of staining in ophthalmology has stimulated us to review the literature and to evaluate dyes which we have employed in our clinic. THEORIES OF STAINING There are numerous theories attempting to explain staining. The probability is that staining is both a chemical and a physical phenomenon. The physical theory accounts for the penetration of the dye