This study aims at testing experimentally the effect of aeration of litter in intensive pig units on nitrogen budget and the nature of nitrogen gaseous emissions. Rearing animals on deep litter provides treatment of these manures at an early stage by composting and aeration of litter could offer a method of controlling the compost temperature and water content. Two aeration systems for the litter (upflow and downflow) were checked against a control system without aeration, over a period of 65 days corresponding to two shortened fattening periods (25-60 kg). Detailed nitrogen balances were obtained, and uncertainties estimated, from which the N2 fraction was evaluated by difference. Rearing animals on sawdust litter enables the removal of nitrogen from the compost as N2 with efficiencies of 44, 53 and 74 ± 13 %, respectively, of total nitrogen excreted for each of the three systems: upflow aeration, downflow aeration and control. The smaller efficiencies of aerated systems with respect to the control are due to the supply of oxygen by aeration. Nitrogen accumulated in the litter is mainly under organic form, and amounts to 19, 27 and 6 ± 1.5 %, respecively, of the nitrogen content of the manure for the three systems. Nitrates only accumulate in the aerated systems (3-7 %). Irrespective of the system, about 30 % of the total nitrogen in the manure was removed as gases N3H and N2O. The NH3/N2O ratio is 1.3 for the control and downflow aeration as opposed to 1.7 for upflow aeration. (© Inra/Elsevier, Paris.)