SUMMARY The total body water and body water turnover in Columbian black-tailed deer (Odocoileus hemionus columbianus) and domesticated sheep (Ovis aries) were compared in winter and summer by testing with tritium oxide (TOH). There was a significant difference in water turnover in both species when data obtained in the winter were compared with those obtained in the summer. In addition, there was significant difference in water turnover between the 2 species in both winter and summer. Deer had a larger body water pool in relation to body weight than did sheep, but rate of body water turnover in deer was slower in both winter and summer. The mean body water pools of sheep in winter and in summer were 53.3 and 46.0% of body weight, respectively. Comparable values for deer were 63.4 and 73.5%. The water flux in sheep was 0.102 and 0.140 L./kg./day in winter and in summer, respectively. Comparable values in deer were 0.053 and 0.104 L./kg./day.