Onchocerciasis is a parasitic disease of man which, in addition to its incapacitating or debilitating effect on the victims, is a major impediment to the economic development of vast areas of riverine land in Africa, Central and South America and Asia. The control programme outlined here recognizes that the problem is complicated by the incidence of malaria and trypanosomiasis of man and animals, and that much of the soil has already become seriously degraded.