During the period I966-69 entomological investigations on the dipterous fauna of grazing cattle in Denmark were carried out with a view to recording potential vectors of the disease "summer mastitis". Some I200 biting midges (Culicoides Latr.) were collected from grazing piebald heifers in 3 field and meadow localities. 8 species of biting midges were represented in the material. Most of the species are known as blood-suckers on domestic animals. About 50 % of the material consisted of C. obsoletus, while C. punctatus, C. chiopterus, and C. subfasciipennis accounted for 24 %, I4 %, and I0 % respectively. Midge activity was extremely high on the belly, especially in the umbilical region and on the udder, much lower on the back and flanks, and considerable on the legs. Several species were present on the belly, however C. obsoletus, C. punctatus, and C. subfasciipennis being dominant. These species could be suspected of participating in the transmission of "summer mastitis", when co-operating with non-biting flies, e.g. Hydrotaea irritans Fall.; they are therefore deserving of special attention. On the back and flanks, C. obsoletus and C. punctatus were the main species, and on the legs, C. chiopterus.