During the storage of solid animal manure, biological transformation of nitrogen (N) and carbon (C) may increase the temperature from 60 to 703C, i.e. composting. Composting may cause emission losses of ammonia (NH ) and carbon dioxide (CO ). Furthermore, plant nutrients may leach from the compost heaps. During a composting period of 197 day from September 1997 to April 1998, emission of NH , nitrous oxide (N O), methane (CH ) and CO was measured using dynamic chambers covering three heaps of deep litter from a house with dairy cows. Leaching of nutrients during composting was determined. Denitri"cation was estimated as N unaccounted for in an N mass balance. The heaps were either mixed once after 30 days, compressed initially or left untreated. Compacting the heap caused a temperature increase from 10 to 50}603C. The temperature increased from 30 to 403C in the heap being mixed. From both the compacted and mixed heap, the cumulative ammonia volatilization was 0)2 kg N/t corresponding to between 2)6 and 3% of the total N. Half of this amount was lost from the untreated heap in which the temperature only increased marginally in the "rst days after the start of the experiment. Cumulative CO losses were 33 (19%), 20 (12%) and 17 kg C/t (10%) from the litter mixed after 30 days, compressed deep litter and untreated deep litter, respectively. Emissions of N O and CH were low. Nitrogen losses due to leaching were (0)8% of the initial N. Total nitrogen losses due to denitri"cation, NH emission and leaching was from 5 to 19% of the initial N, the lowest from mixed and the highest from untreated litter.