The potential reduction in nitrogenous excretion by growing pigs, through the reduction of protein levels in diets, has not been consistently achieved without compromising performance. This may have been due to inadequate formulation of the diets. Formulation on the basis of the total amino acid content of feed ingredients may limit the nitrogen retention, and hence the rate of protein accretion (Lee et al., 1993). Therefore, the objective of the experiment reported here was to evaluate the nitrogen balance of pigs fed diets at two levels of protein, formulated on the basis of true ileal digestibility of the essential amino acids (Rhône-Poulenc Animal Nutrition, 1993) and the net energy available from the raw materials (Noblet et al., 1994).