It is estimated that ammonia emission from pigs contributes approximately 23kt of a total of 198kt from UK agriculture. Of this, 14kt is lost from buildings and 7.5kt from land spreading. It is likely that pig enterprises will need to reduce ammonia losses under the newly adopted Integrated Pollution Prevention Control (IPPC) legislation. Earlier work (Kay and Lee, 1996) has demonstrated that low crude protein (CP) diets reduce the amount of nitrogen in slurry. However, there is no information available on the effects of reducing nitrogen excretion by pigs on the emission of ammonia from buildings and limited information on the effects of collection and storage of slurry over time. The objective of this experiment was to determine the effect of low CP diets on the emission of ammonia from buildings, and on the characteristics of slurry collected and stored beneath slats.