The aim of the experiment was to determine the potential for the improvement of growth performance and reduction of nitrogen excretion in chickens by formulating practical diets, with or without meat-and-bone meal, on a digestible amino acid basis. From days 22 to 42 chickens were fed isoenergetic diets based either on maize, wheat and soyabean meal and containing 8% meat-and-bone meal (M) or on maize, soyabean meal, rapeseed meal and faba beans (P). Diets were formulated on a total (Mt and Pt) or digestible (Md and Pd) amino acid basis. No significant differences in performance indices between chickens fed M diets and those fed P diets were obtained. Mean daily N output on diets containing exclusively vegetable ingredients was significantly lower than on M diets. A similar trend was observed for relative N output (% of N intake). Body weight gain, feed conversion ratio, and European Performance Index value of chickens fed diets formulated on a digestible amino acid basis were superior (P ≤ 0.05) to those of chickens fed diets based on total amino acids. There was a tendency for both measures of N output to decrease when diets were formulated on a digestible amino acid basis.