Two advanced methods for identification of Listeria monocytogenes strains: a commercial miniaturised biochemical test - API®LISTERIA (bioMérieux) and polymerase chain reaction (PCR) adapted to the in vitro amplification of the iap gene fragment (453 bp), were used in comparative studies. A total of 63 strains suspected, based on morphological criteria, to belong to L. monocytogenes species were subjected to both identification procedures, with 58 strains (92.1%) being of the river water, fish, fish products, ingredients used in fish production and the fish-processing environment origin. Comparison of the results showed that 87.3% strains were recognised as L. monocytogenes with both tests and expressed haemolytic activity. The PCR enabled to classify 3 strains of uncertain biochemical identification. Two non-haemolytic strains were confirmed to be L. monocytogenes with both tests. In the case of the third non-haemolytic isolate, the results of both tests were contradictory. None of the analysed strains remained unidentified. Simultaneous application of both identification methods proved to be particularly useful in microbiological diagnosis of food.