An experiment was conducted to determine the apparent ileal amino acid digestibilities in hulled and hulless barley, in addition to energy digestibility which was also determined with the in vitro method. Seven barrows, fitted with a simple T-cannula at the distal ileum, were fed seven diets (180 g CP kg^-1) according to a 7 × 7 Latin square design. The basal diet consisted of maize starch and soyabean meal (SBM). The other diets (diets A to F) contained both SBM and barley. Diet A: hulled barley, c.v. Harrington I. Diet B: hulled barley, c.v. Harrington II. Diet C: hulless barley, c.v. CDC Buck I. Diet D: hulless barley, c.v. CDC Buck II. Denotations I and II are given to indicate two different origins of Harrington and CDC Buck. Diet E: mixture of c.v. Harrington I and c.v. CDC Buck I (50:50 wt/wt). Diet F: mixture of c.v. Harrington II and c.v. CDC Buck II (50:50 wt/wt). The mixtures were created to establish linear regression equations between the in vivo and in vitro energy digestibility values. Chromic oxide was used as the digestibility marker. The barrows were fed twice daily, at 08.00 and 20.00 h. Each experimental period comprised 10 days. Faeces were collected from 08.00 on d 6 to 08.00 on d 8. Ileal digesta were collected from 08.00 on d 8 until 08.00 on d 10. The initial and final average body weights of the barrows were 35 and 90 kg, respectively. The amino acid and energy digestibility values were determined with the difference method. The apparent ileal amino acid digestibility values were lower (P < 0.05) in hulless than in hulled barley. The digestibilities of lysine and threonine (first- and second-limiting amino acid in barley) ranged from 58.2 to 59.4% and from 53.7 to 55.6%, respectively, in hulless barley and from 62.6 to 69.7% and from 57.4 to 59.6%, respectively, in hulled barley. The energy digestibility values ranged from 86.4 to 87.6% in hulless barley and from 79.9 to 81.1% in hulled barley. There was a close correlation (r² = 0.88) between the in vivo and in vitro energy digestibility values.