1. The heat tolerance and walking performance of bulls, steers and heifers exposed to moderate heat stress have been compared, following the method of Yeates & Murray (1966). Hereford cattle aged 14–16 months were used in the experiment. Two speeds of walking were employed and the effect of clipping the coats of both exercised and stationary cattle was studied.2. In the undipped state, at both speeds of exercise (1⅔ and 2⅔ m.p.h.), the heifers performed best followed by the steers and bulls in that order, judged by their ability to preserve normal body temperature.