True ileal lysine digestibilities were determined using the homoarginine (HA) method in casein-, barley-, canola meal-, and barley-canola meal-based diets fed to growing pigs. Four Yorkshire barrows (25 to 49 kg BW) equipped with ileal T-cannulas were fed one of the diets according to a 4 x 4 Latin square design. All diets, except for the barley diet, were formulated to be similar in DE:CP ratio. Ileal digesta were collected continuously for 24 h on d 7 and 9 of each experimental period for determining apparent and true ileal digestibilities, respectively. True ileal lysine digestibility and endogenous flows were determined by feeding diets in which 50% of the protein-containing ingredients was guanidinated; the conversion of lysine to HA allows for direct determination of true lysine digestibilities. The apparent ileal CP and amino acid digestibilities were higher (P < .05) in the casein diet than in the barley, canola meal, and barley-canola meal diets. The CP digestibility was higher (P < .05) in the barley-canola meal diet than in the barley and canola meal diets. Endogenous lysine losses were influenced by diet (P < .05) and ranged between 586 and 1,429 mg/kg DM intake. True ileal lysine digestibilities in barley, canola meal, and barley-canola meal diets were similar (P > .05) and lower (P < .05) than in the casein diet. The true ileal amino acid digestibilities were estimated for other amino acids. Unlike apparent digestibilities, true digestibilities seemed additive in the barley-canola meal mixture.