A review, with 63 refs., of recognition of the N-nitrosamines formation mechanisms in various matrices, such as biolog. samples, surface and drinking waters, cosmetics, active substances or pharmaceutical products, and the criteria for detg. them at very low concn. The use of the MS detector and tandem mass detector in HPLC and GC allowed for the development of sensitive methods for the detn. of nitrosamines at a very low level, using appropriate techniques of isolation and enrichment of analytes.