Results of oral and topical erythromycin therapy in 41 infants under 4 months of age with chlamydial conjunctivitis were evaluated in randomized clinical trial. After three weeks of treatment, relapse or reinfection of the eye occurred in four of 19 patients (21%) in the topical therapy group and in three of 22 patients (13.6%) in the oral therapy group (p less than .69). In the topical therapy group, chlamydiae were isolated from nasopharyngeal cultures of eight patients (42%) during or after therapy. Chlamydiae were eradicated from the nasopharynx of the six colonized patients treated with oral erythromycin. All relapses responded to a course of oral erythromycin therapy. We conclude that both modes of therapy are comparable for treatment of chlamydial conjunctivitis, but that oral therapy has the advantage of eradicating nasopharyngeal colonization.