Nitrogen balance in pig farms of the Walloon Region: between quality of production and environmental constraints. During the year 2002 and 2003, 21 pig farms were audited using the Ecoferme software. This software uses data commonly available at farm level to calculate nitrogen stocks and fluxes within the farm and between the farms, the environment and other enterprises. The farms were of three groups according to their specifications in pig production: organic farms, labelled farms and conventional farms. The results are given in relation to the nitrogen directive of the European Union and the Walloon right. This comparison gives information on nitrogen uses in the three contrasted pig production chains in the Walloon Region. This article shows that the environmental performances of pig farms vary strongly within the groups. Nevertheless, it shows that, even if the majority of the farms reached a target above the political goals, the labelled farms have the best global results.