Vancomycin is an antibiotic which is especially active against Gram positive bacteria. At present, numerous infections of the anterior segment of the eye are caused by the Staphilococcus aureus and epidermis. Strains which are resistant to methicilin are more and more frequent and for this reason Vancomycin is becoming the antibiotic of choice to combat these infections since no resistance of the Staphilococcus to it has been demonstrated. The authors evaluated the levels of Vancomycin in aqueous humor after the administration of topical eye-drops. For the first two hours after the last administration, levels of 0.52 micrograms/ml were detected. These inhibit the growth of the majority of bacteria sensitive to Vancomycin. Between two and four hours, the levels decreased to 0.15 micrograms/ml; these are therapeutic levels for a large number of Gram positive bacteria. From four hours after the last administration, these levels are undetectable. Due to the success of its penetration, topical administration of Vancomycin should be considered as a therapeutic modality against infections by gram positive bacteria of the anterior segment. The ideal guideline for administration would be one drop every two hours, especially if the infection is severe. In this way, subconjunctival injection could be avoided.