A method is described whereby tsetse visiting a stationary ox can be observed through a one-way glass screen in the presence or absence of man. Under the latter condition six times as many adults of Glossina pallidipes Aust. perch and feed on the ox. In G. morsitans Westw. most flies land in the head-down position and are unaffected by man's presence, but in the absence of man there is a four-fold increase in the number which land and feed in the head-up position. Calculations indicate that in the absence of man virtually all G. pallidipes adults attracted to the ox alight on it, and nearly all attempt to feed. Man's presence not only repels many tsetse completely but also inhibits the landing response of many of those that do approach the ox.