A laboratory scale biofilter was designed to study the removal of gaseous ammonia. The filter was constructed from perspex - 0.6 m in height and 0.2 m inner diameter. Peat granules were used as the packing material. The biofilter was operated at ambient temperature. Ammonia was supplied to the system in a discontinuous mode. The moisture level in the system was maintained at 40 - 60% by humidification of the inlet gas stream and by sprinkling the peat bed with water. The pH of the system fluctuated between pH 6.10 and pH 8.98. There were three stages of biofilter operation, during which ammonia was supplied discontinuously at concentrations of 14 mg m’3, 565 mg m'3 and 2260 mg m"3 respectively. Ammonia was removed from the air with at least 90% efficiency even when high loads were supplied. However, up to 40 % of the ammonia supplied was removed by adsorbance on to the peat. There was also evidence of nitrification. Although bacteria and fungi were detected on the native peat there were no nitrifiers and therefore the peat was inoculated with nitrifying activated sludge. Throughout biofilter operation peat samples were taken from the top of the filter and from sample ports at 0.2 m and 0.4 m of the filters’ height for microbial *5171 analysis. The total bacterial counts increased from 10 cfu g" peat to 10 cfu g' peat. However, the numbers of both fungi and nitrifying bacteria decreased overall.