A new long-acting sulfamide, Ro 4-4393, has been assayed in the treatment of 350 trachomcitous children frorn endemic areas, in comparison to the local use of antibiotic ointments. Different schemes of administration were adopted, posology ranging between 20 to 50 mg/kg body weight, in weekly, fortnightly and monthly intervals, and as a single dose. The results obtained with most of the therapeutic schedules were at least comparable to those given by topical antibiotics. The period of control is still too short for definite conclusions, and the authors suggest the study of new groups treated with Ro 4-4393.