The general characteristics of Onchocerca volvulus infection and its transmission are outlined in this overview of human onchocerciasis. The pathogenic role of the microfilariae, producing lesions of the skin, lymphatic system, eye and deep organs, are described, along with the main clinical manifestations of the disease. The global prevalence and distribution of onchocerciasis are given. Best estimates in 1985 gave 86 million persons at risk, 17.8 million infected, 336,400 blind and a like number suffering from severe visual impairment. The vast majority was in Africa. The impact of onchocerciasis on communities in the Sudano-Guinean savanna zone of Africa is outlined, emphasizing the very high blindness rates and the increased mortality among the blind. Communities so affected cannot remain economically viable. They are forced to desert their villages and the fertile land near rivers. The background to the establishment of the Onchocerciasis Control Programme in West Africa (OCP) is given and the successful 10-year results of this campaign, which is based on prolonged, regular Simulium larviciding, are outlined. In the context of the future of the OCP and of the control of onchocerciasis elsewhere in the world, the need for improved chemotherapy is discussed. The prospects for large-scale suppressive therapy have greatly improved following the registration of ivermectin in 1988 for use in human onchocerciasis. The potential and possible uses of this drug, as a single-dose, non-toxic microfilaricide, which excites very little Mazzotti reaction and has a prolonged microfilarial suppressant action, are discussed. It is considered that an effective non-toxic macrofilaricide is still a prime need for onchocerciasis control.