Two experiments each with two rates of feeding (maintenance and twice maintenance) were conducted during summer 1993/94 (Expt 1) and summer 1994/95 (Expt 2), at Massey University, New Zealand. Four sambar and four red deer, including stags and hinds aged 10–14 months, were used in each year. Animals were fed a pelleted diet (total N 30 g/kg DM; NDF 247 g/kg DM). Digestibility and nitrogen (N) balances were determined using deer metabolism cages, whilst methane production and heat production were determined using open circuit respiration calorimetry, with measurements made on each deer at both rates of feeding. Digestibility and metabolizability of energy were greater for sambar than for red deer in Expt 1 but not in Expt 2. Nitrogen retention, expressed as a proportion of N intake, was similar for sambar and red deer. Metabolizable energy required for maintenance (MEm) was 474 kJ kg W−0·75 d−1 for sambar deer and 567 kJ kg W−0·75 d−1 for red deer, whilst the efficiency of utilization of ME above maintenance (kg) was similar for sambar deer and red deer. These studies indicated that the sambar deer had lower rates of maintenance heat production than the red deer, which may explain the sambar's superior feed conversion measured in previous experiments. However, the two species utilized nitrogen with similar efficiency, when fed a high quality ration.