Because topical antibiotic treatment has had a limited effect in previous controlled trials against trachoma, treatment with oral erythromycin was compared with topical tetracycline in 6-8-year-old children in southern Tunisia who had potentially blinding active trachoma. A total of 169 children were divided into two groups that were carefully matched for age, sex, locality, and intensity of disease. Oral erythromycin ethyl succinate in a paediatric dosage form was administered to one group and topical 1% tetracycline ointment to the other group, twice daily, six days a week for three weeks. The two treatments were equivalent in effectiveness and resulted in a substantial decrease in disease intensity and a marked reduction in chlamydial infection detected in conjunctival smears. To maintain blood levels of antibiotics known to be effective in the treatment of chlamydial infections with a dosage schedule possible in a trachoma control programme, one of the long-acting tetracyclines (doxycycline or minocycline) might be considered. Such systemic chemotherapy should be limited to selective treatment of individuals who can be adequately monitored.