The purpose of the present study was to evaluate the level of vancomycin in human aqueous humour after intravenous (i.v.) and subconjunctival administration. One hundred patients scheduled to undergo cataract extraction participated in the study. Fifty-three of them received 20 mg vancomycin subconjunctivally and 47 received two doses of vancomycin i.v. (1 g b.i.d.). Specimens of aqueous humour from the first group were collected 1, 2, 2.5, 3, 3.5, 5, 6, 7, and 8 h after the subconjunctival injection. In the second group, specimens of blood and aqueous humour were collected 1, 2, 4, 6, 8, 10, and 12 h after the end of infusion of the second dose of the antibiotic. The levels of vancomycin were determined by fluorescent polarization immunoassay. In the first group peak levels of 24.82+/-3.55 microg/ml were achieved in aqueous humour at 5 h, whereas in the second group peak levels of 1.42+/-0.47 microg/ml were detected at 6 h. The latter levels, although higher than the MICs of most of the Gram-positive pathogens causing eye infections, are inadequate for the treatment of infections in vivo. These results support the need for subconjunctival instead of i.v. administration of vancomycin in order to achieve therapeutic levels of the drug in human aqueous humour or for prophylactic use whenever indicated.