The endemicity of human onchocerciasis was assessed in eight rural, at-risk communities in Ningi Local Government Area, Bauchi State, Nigeria, between July 1990 and March 1991. Of the 1536 subjects skin-snipped, 334 (21.7%) were positive for Onchocerca volvulus microfilariae. Surprisingly, there was a significant inverse relationship between prevalence and mean microfilarial load (r = -0.608; P < 0.05). Males were more likely to be infected than females (P < 0.01) and cattle rearers (71.0% infected), farmers (49.8%) and fishermen (40.0%) had significantly higher prevalences than students/schoolchildren, housewives or traders (P < 0.001). Pruritus and itchy eyes were recorded in all age groups and appeared in much younger subjects than any other manifestations of the infection. Prevalence and onchocercal blindness were linearly related to intensity of infection. The epidemiological significance of these findings, in terms of a future community-wide programme of long-term chemoprophylaxis with Mectizan, is highlighted.