Two experiments were conducted to evaluate the relevance of formulating pig diets according to apparent ileal digestible amino acid contents. In Exp. 1, six pigs were fitted with post-valvular T-caecum (PVTC) cannula in order to determine apparent ileal digestibility of crude protein (CP) and amino acids of soyabean meal (SBM), rapeseed meal (RSM), maize (M), wheat (W) and barley (B). In Exp. 2, two consecutive balance trials were performed with four groups of six male pigs (Polish Landrace) of initial body weight of about 28 kg. Pigs were fed according to their metabolic BW with four diets differing in CP levels, formulated on the basis of ileal digestible amino acid content, according to Dutch recommendations (Voedenormen Landbouwhuisdieren, Centraal Veevoederbureau, No. 18, Lelystad, The Netherlands, 1995). Two diets containing low (L-SBM) and high (H-SBM) protein level: 151 and 165 g/kg, respectively, were composed of soyabean meal, maize and barley, and two other diets containing also low (L-RSM) and high (H-RSM) protein level: 161 and 175 g/kg, respectively were composed of rapeseed meal and wheat. In Exp. 1, distinct differences were found between SBM and RSM in their digestibilities of CP (77.0 and 59.5%, respectively) and all amino acids. Among the cereals, CP digestibility and that of most amino acids were the highest for wheat and the lowest for barley. In Exp. 2, urinary N excretion, expressed in percent of intake, was the highest in pigs fed on diets H-RSM (36.2%) and L-RSM (37.0%) and was the lowest on diet L-SBM (30.1%). Accordingly, N retention was lower ( P<0.001) after feeding rapeseed than soyabean meal diets (on average 47.5 and 52.2%, respectively). Daily N retention ranged from 20.0 g (L-RSM) to 22.9 g (H-SBM), and these values differed at P<0.05. Possible factors affecting balance differences are discussed.