Continued improvement through genetic selection and the use of entire males has resulted in pigs with considerable potential for lean tissue growth rate. These animals have, however, lower appetites and this suggests that there may be considerable differences in the partition and in the efficiency of utilisation of dietary nutrients, compared with those previously recommended by ARC (1981). There may also be differences in energy expenditure since Campbell and Taverner (1988) and Rao and McCracken (1990) have suggested that animals of high potential for lean tissue growth rate have higher maintenance energy requirements. There is little information on the energy requirements of pigs of different growth potential and the present experiments were designed to evaluate the effects of feeding levels on nutrient partition and energy metabolism of pigs of different body weights and sex.