Two hundred fifty six broiler chickens, 22-days-old, allocated to four groups of four replicate pens with 16 birds each, and six adult ileostomized roosters were used. Four diets containing maize starch and 550 g/kg whole or 458 g/kg dehulled lupin seeds (Lupinus luteus L. cv. Amulet) as the only protein source were offered to birds with or without α-galactosidase supplementation. The apparent ileal digestibility of dry matter and nitrogen of the diets was determined. In chickens digesta was collected from the lower part of the ileum immediately after slaughter, while in roosters digesta was collected via a T cannula placed in the terminal ileum during three 12 h periods in a change-over design. Dehulling of lupins significantly increased apparent ileal digestibility of dry matter of the diet by 10% in roosters (P<0.01) and 14% in broilers (P<0.001), while α-galactosidase supplementation increased DM digestibility by 3% only in roosters (P<0.05). Dehulling of lupins increased the apparent ileal digestibility of N only in roosters (P<0.01). There was no difference between roosters and broiler chickens with regard to the DM digestibility, but the apparent digestibility of N was lower in roosters, than in broilers. The viscosity of ileal digesta was measured only in chickens. It was generally low and was highest (2.92 mPas.s) in broilers fed the whole lupin diet without α- galactosidase. Viscosity was about 37% lower after dehulling the seeds, and decreased about 15% after α-galactosidase supplementation.