During the fermentation of silages from nitrate-rich grass, the conditions are suitable for the formation of N-nitrosamines. Earlier investigations had shown that only low concentrations of volatile N-nitrosamines were formed. The first ten days of ensilage were investigated. The formation of nitrite was accompanied by the formation of volatile N-nitrosamines. NDMA and NDEA were detected in concentrations of up to about 2 micrograms/kg. After stabilisation of the silage, these concentrations dropped to about 0.6 microgram/kg. Preliminary results are presented concerning the presence of non-volatile N-nitroso compounds. The method of Walters et al. (1980) indicates that non-volatile N-nitroso compounds were present in amounts equivalent to 85 mg NPIP/kg sample.