This audiovisual describes in detail the life cycle of the Onchocerca volvulus and its role in causing blindness in Ghana. Clinical examples of persons afflicted with this disease are shown to elucidate the effects of the disease. According to the presentation, the disease is transmitted by the bite of black flies of the family Simuliidae. The method by which the flies acquire the organism is carefully outlined, as is the process by which the infective larvae enter the wound and develop into male and female worms, which mate and cause a tissue reaction in man. This reaction produces fibrous nodules which often appear externally as lumps. If ocular invasion occurs, blindness can result. Treatment of the disease by surgical removal of the nodules or by administration of the drug diethylcarbamazine is discussed. Measures to control the breeding grounds of the flies with DDT are also noted.