43 species and 3 "varieties" (sensu Fairchild) of horseflies (Diptera: Tabanidae) were collected in Maracá Island and in the Pacaraima hills, Roraima, Brazil. Fidena schildi (Hine), Esenbeckia prasiniventris (Macquart) and Tabanus unimacula (Kroeber) are registered for the first time in Brazil and two new species are described: Catachlorops bindai and Stypomnisa vidali. The male of Tabanus sannio Fairchild ir described. Some ecological data are presented.