This study was conducted to examine if the use of dual digestibility markers as well as differences in neutral-detergent fibre (NDF) contents and dietary crude protein (CP) and amino acid (AA) levels were responsible for the large variability of apparent ileal AA digestibility values in barley samples for growing-finishing pigs. Six barrows, with average initial and final body weights of 30.5 and 58.6 kg, were fitted with a simple T-cannula at the distal ileum and fed six barley-based diets at close to ad libitum feed intake according to a 6 × 6 Latin square design. The six diets contained 97% barley samples varying in CP and AA contents. Chromic oxide (Cr₂O₃) and acid-insoluble ash (AIA) were used as digestibility markers. Each experimental period consisted of 7 d. Ileal digesta was collected at 2-h intervals for a total of 24 h. There were large differences (P < 0.05) in the apparent ileal CP and AA digestibility values among the barley samples as determined by both the Cr₂O₃ and the AIA markers. The use of Cr₂O₃ and AIA markers and differences in NDF contents had no effects (P > 0.05) on the variability of the apparent ileal CP and AA digestibility values among the barley samples. The use of the dual digestibility markers had no effects (P > 0.05) on the determination of apparent ileal CP and AA digestibility values in the majority of the diets. Differences in dietary CP and AA contents were primarily responsible for the large differences (P < 0.05) of the apparent ileal CP and AA digestibility values among the barley samples. Apparent ileal CP and AA digestibility values determined in barley samples are not reliable and should not be used in diet formulation for pigs. True ileal CP and AA digestibility values directly determined from various barley samples should be used in diet formulation for pigs.