Several authors have reported corneal and retinal changes occurring during high-dosage application of chloroquine for the treatment of some internal and dermatological diseases (300-500 mg of the base daily). The critical limit seems to be application of a total of 100 g of the base of chloroquine. In malaria prophylaxis (300 mg of the base weekly) it will take six-and-a-half years to reach this limit. In the few reports (27 cases) of ocular damage following malaria prophylaxis, a hyperdosage became evident. People living for prolonged periods of time in areas where malaria is endemic should have regular ophthalmological examinations and the administration of chloroquine should be stopped at the slightest sign of ocular damage.