The faunal composition and seasonal changes in the tabanid fly population were investigated at two adjacent pastures : one in the plain and the other in the mountain of northern Tochigi.
　The survey was performed during the period of 1978-1981 by sampling with a sweeping net from cattle and/or a mosquito net trap with CO₂-baited.
　At the plain pasture, the tabanid fauna comprised 11 species and 2 genera, of which Tabanus nipponicus and Atylotus bivittateinus were predominant. The former occupied 60% of the total specimens showing a marked peak in early July and the latter 37% with a peak in August.
　At the mountain pasture, 21 tabanid species composed of 6 genera were collected in total. Among them, the most dominant species was T. nipponicus (75% of the total number) , followed by T. chrysurus (9%) and T. rufidens (6%). They were most active in July to August.
　Tabanid faunal composition at mountain pasture seemed to be richer than at plain pasture on account of more diverse environments.