About two thirds of the total nitrogen intake of pigs is excreted as liquid and solid wastes and gaseous ammonia. The pollution potential is such that it places limitations on the development of pig production. One approach to reducing pollution may be to minimize nitrogen output through manipulation of protein feeding whilst maintaining an optimum level of production performance. A model has been constructed for predicting nitrogen excretion by pigs which applied to breeding stock and growing and finishing pigs under French conditions. The principles of mathematical models for predicting protein and amino acid requirements in growing pigs and sows have been developed. The first growth and digestibility trials have been completed for minimizing total dietary protein input in combination with improved amino acid balance while maintaining optimum performance. The effect of dietary protein level on slurry loading and ammonia emissions is being assessed. A first evaluation has been made at the farm level of the economic impact of decreasing nitrogen output through protein feeding.