321 adults living in an hyperendemic onchocerciasis focus in North-Cameroon who received a first dose of ivermectin (150 micrograms/kg) in 1987 and a total of three, four or five doses from 1987 to 1991 were parasitologically examined in 1992. The prevalence of skin microfilariae (PMf) and the geometric mean microfilarial load (GMMf) were respectively reduced by 33 and 97% from the initial values in the group of subjects who received five treatments. In 1992, the PMf and the GMMf were not significantly different in the groups which received three, four or five doses of ivermectin. It is not necessary to achieve an important drug coverage to maintain a tolerable level of infestation in the community.