Urban epidemics of Oropouche (ORO) fever in three municipalities in Pará, Brazil were studied in 1975. Culicoides paraensis (Goeldi) were collected during each of the epidemics and there was a positive correlation, by study areas within the city of Santarém, between human seropositivity to ORO virus and population densities of C. paraensis and Culex quinquefasciatus Say. The best numerical correlation was with populations of C. paraensis. The relative absence of other species in the areas of high disease attack rates was further evidence C. paraensis were the probable vectors of ORO virus. These biting midges were found to bite readily inside of houses, with an indoor/outdoor ratio of 29%, and were most active around 1700–1800 hours. Other biological observations on C. paraensis are presented.