Egg masses of the horse fly, Hybomitra nitidifrons nuda (McDunnough), and the deer fly, Chrysops aestuans Wulp (Diptera: Tabanidae), were collected during the summers of 1996–2000 from five different locations in southern Manitoba. On average, hymenopterous egg parasitoids were reared from more than 90% of collected egg masses. Telenomus hybomitrae Iranpour and Galloway and (or) Telenomus utilis Iranpour and Galloway (Hymenoptera: Platygastridae: Telenominae) emerged from multilayered egg masses of H. n. nuda. However, Trichogramma semblidis (Aurivillius) (Hymenoptera: Trichogrammatidae) and (or) Telenomus chrysopsis Iranpour and Galloway were reared from single-layered egg masses of C. aestuans. In H. n. nuda egg masses, more than 33% of individual eggs were parasitized and more than an additional 35% were apparently damaged by the two telenomine parasitoids. In C. aestuans egg masses, approximately 40% of individual eggs were parasitized and 18% produced neither parasitoids nor larvae.