The report presents the RIVM methodology for calculating the emission of ammonia. Four ammonia sources, animal manure, application of fertilizer, industrial processes and households, are distinguished. The ammonia emissions in the Netherlands in the period 1990-1992 are respectively 215, 221 and 170 million kg. The 1992 emissions are presented on a 5 x 5 km grid in the report. The enforced legislation for low emission techniques both for grassland and arable land forms the main reason for the decrease of the 1992 ammonia emission by 50 million kg.