The good results of penicillin in treatment of some experimental intraocular infections of the anterior segment of the eye1and the antibacterial activity of penicillin in vitro against most organisms found in intraocular infections suggested the study of the penetration of penicillin into the anterior chamber. The investigations on the topical use of penicillin deal, first, with the entrance of penicillin into the aqueous of rabbits after iontophoresis as compared with that after the corneal bath ; second, with the influence of wetting agents on the penetration of penicillin, and, finally, with the possibility of its introduction by repeated use of solutions or ointments with and without wetting agents. The studies on the systemic application are limited to determinations of penicillin in the blood, the spinal fluid and the intraocular fluids after single intramuscular injections. The penicillin used in these experiments was obtained from a strain of Penicillium notatum grown