A study was carried out in Bauchi from July 1990 to April 1991 to investigate the heat tolerance of Yankasa, Uda, and Balami breeds of sheep. Rectal temperature (RT), respiration (RR), and pulse rates (PR) were taken on five animals from each of the three breeds. There were significant (P < 0.05) differences between Yankasa and the other breeds (Uda and Balami) in RT (39.6°C, 39.7°C, and 39.7°C), RR (62.2, 64.9, and 66.0 breaths per minute), and PR (74.8, 76.9, and 77.1 beats per minute), respectively. The Heat Tolerance Coefficient (HTC) and Coefficient of Adaptability (CA) were 86.86, 86.38, and 85.66, and 3.80, 3.85, and 3.91 for Yankasa, Uda, and Balami, respectively. Significant (P < 0.5) differences existed between breeds in HTC but not in CA. There were significant (P < 0.05) differences between males and females in RT (39.6°C and 39.7°C), RR (64.30 and 65.09 breaths per minute), PR (76.18 and 76.77 beats per minute), and HTC (86.83 and 85.90), respectively, but no appreciable difference was observed in CA between sexes. Significant (P < 0.05) differences existed between season in RT, RR, PR, HTC, and CA. The combined effects of temperature and humidity had a greater influence on the animals than their separate effects. An increase in respiration rate appeared to be the immediate response of sheep to environmental stress. Generally, the Yankasa breed was more heat-tolerant than the Uda and Balami breeds.