The review summarises the contemporary knowledge on occurrence, production, and estimation of different microbial nitrate reductases (NR). The main interest is focused on two basic NR types: dissimilatory and assimilatory NR, both playing an important role in nitrate metabolism of bacteria. NR are putatively responsible for the presence of nitrosamines in many food items. In the second part, quantitative and qualitative methods of NR estimation are compared.