A procedure for the ileostomisation of adult roosters has been described with the use of flexible silicon cannulas. Apparent ileal digestibility coefficients for dry matter (aDC DM), crude protein (aDC CP) and amino acids (aDC AA) in six diets, formulated with maize, wheat gluten, faba beans, lupins, soybean meal and casein as the main protein sources were determined in the ileostomised roosters fitted with silicon cannulas. In addition, aDC data determined using roosters (present study) were correlated with previously published aDC data of the same diets determined with pigs [van Leeuwen et al. (1996a). Apparent dry matter and crude protein digestibility of rations fed to pigs and determined with the use of chromic oxide (Cr203) and linsoluble ash as digestive markers. Br. J. Nutr. 76, 551-562; van Leeuwen et al. (1996b). Validation of a mathematical model to explain variation in apparent ileal amino acid digestibility of diets fed to pigs. J. Anim. Feed Sci. 5, 303-315]. The ileal aDC CP in roosters ranged from 0.81 to 0.92. Significant (P<0.05) differences in aDC CP and aDC AA were observed between diets. Between aDC in roosters and pigs linear relations were found. The linear models explained 85% of the variation in ileal aDC CP between the six diets determined in roosters and pigs. For ileal aDC AA, the explained part of the variation between roosters and pigs, ranged from 62 to 96%, depending on the particular amino acids, with the exception of aDC of Arg. The standard errors (S.E.) of the models for the prediction of the aDC AA in roosters from aDC AA of the pigs was <0.04 units.