A revision is made of the previously poorly studied blackfly fauna from the south-western border of Guyana with Brazil. Notes on the biosystematics of the species found are provided, together with keys and illustrations based on their morphology. Of the 14 species recorded, eight are anthropophilic and two of these ( Simulium oyapockense
and S. guianense s.l.
) are proven vectors of human onchocerciasis in the nearby Amazonia focus of the disease in neighbouring Brazil.