1. The endogenous energy (EEL) and nitrogen losses of adult cockerels were studied during both when the animals were starved and when they were fed on a highly digestible nitrogen-free diet. The birds were fed three intakes by intubation and the effects of these intakes were compared. 2. During the 48-h study, the excretion of energy (EEL) was found to be 49.4 kJ, when the birds were given food. When starved this estimate was considerably higher, 70.3 kJ. 3. When endogenous energy per 48 h was corrected to zero nitrogen balance (EEL0), the value of starved animals of 30.1 kJ was still considerably higher than the 13.4 kJ for fed birds. 4. It was concluded that feeding a nitrogen free, highly digestible diet reduces the excretion of endogenous energy. Thus determinations from starved birds appear to give biased estimates of EEL and EEL0. Hence, true metabolisable energy values would also be overestimated where endogenous energy values from starved birds were used.