It has been noted in many parts of the world that bacterial conjunctivitis is a major cause of total or partial loss of vision. In addition, trachoma is aggravated if there are associated bacterial infections and these lead to more frequent corneal complications.In the trials described the seasonal variation of bacterial infections was studied in addition to trachoma in 3 pilot sectors in southern Morocco. The frequency of complications and late sequelae from these infections in the whole population of these sectors was also studied.In one of the sectors 3 different methods of limiting the regular seasonal increase in bacterial infections and of curing trachoma were evaluated separately or in combination. These included the effect of fly-suppression on the transmission of infection, a possible method of chemoprophylaxis, and intermittent treatment with chlortetracycline ointment.The effect of the latter, when applied to a whole population group by auxiliary personnel, was compared with the long-term effect of self-treatment, in this and the two other sectors.The total observation period covered 12 years.