In a model experiment, dual-purpose type chickens (Barret Rock×New Hampshire) were allocated to 4 groups with 5 replications of 4 males and 4 females. For the first (1-49 days) and second (50-83 days of age) period of feeding, the chickens were fed diets composed of feeds approved for organic production. The diets for both periods contained lower (20 and 18%) or higher (22 and 19%) levels of crude protein, 0.36 and 0.25% or 0.38 and 0.28% of total methionine, and 0.66 and 0.57% or 0.70 and 0.61% sulphur amino acids, respectively. Diets were supplemented or not with DL-methionine (Met). In the last week of each period, feed intake was determined, excreta were collected for N-balance calculation. Body weight gain, feed intake, feed conversion and mortality were estimated and production index values calculated. On day 83 of life, 4 males and 4 females were killed and slaughter analysis was performed. The higher dietary crude protein level increased feed intake and worsened feed conversion in the first and second period of feeding and increased feed intake for the whole experiment. Met supplemented to the diets positively affected body weight gain, feed conversion and production index in the second and entire feeding period. It also increased breast meat yield and decreased abdominal fat content in carcass. Increased N-excretion and N-retention at the higher level of dietary crude protein and the positive effect of Met supplementation on nitrogen utilization did not reach statistical significance (P>0.05). Nevertheless, for the whole period of feeding, Met added to the diet reduced nitrogen pollution of the environment from dual-purpose type chickens for a total 4.7 to 4.9 g/chick/83 days.