1. Heat production was measured for about 24 h at six temperatures from 2 to 35 °C on individually starved broilers that had been subjected to four treatments; these were acclimated or unacclimated to these temperatures, or to these temperatures for 12 h and to 22 °C for 12 h (alternated) during each 24‐h period.

2. Response curves relating heat production and environmental temperature for the four different treatments differed significantly. Only the unacclimated birds subjected to the alternated temperatures increased heat production at 35 °/22° C. Major effects of acclimation were observed mainly in the cold.

3. The relationship between daily endogenous nitrogen (N) excretion and heat production (mg N/kJ) was constant at the different temperatures, but acclimation and alternating temperature increased N excretion.

4. Evaporative heat loss was reduced by alternating temperature at the high temperatures, and by maintaining temperature constant in the cold.