Body heat storage changes of cattle were measured by means of simultaneous direct and indirect calorimetry and by thermometry in an environment that alternated in temperature between 12 and 25 °C. When the calorimeter temperature was increased deep body temperature (T c ) increased by approximately 0-5 °C, mean surface temperature (T t ) by 3 °C and mean body temperature (determined from calorimetry, T s ) by 1 °C, but these increases were not fully sustained during the next 24 h. Changes in the three temperatures were related by the equation: AT b = a.AT c + (l -a) AT S where a was found to be 0-89+ 0027 (S.E.).