Contrary to volatile N-nitrosamines, about mechanism of decomposion of apparent total N-nitroso compounds and non-volatile nitrosamines e.g. N-nitrosoaminoacids in beer is known only a little. In the first part of this article are therefore given the basic information about their incidence, mechanism of arrising and method of estimation in beer and other foodstuff. The second part of this article is dedicated to the study of the efect of UV irradiation on the ATNC and their some components N-nitrosoaminoacids nitrososarkosine (NSAR), nitrosoproline (NPRO and the main representative of volatile N-nitrosamines N-nitrosodimethylamine (NDMA) in beer. The purpose of this study was to assign previously unknown contents of selected nitroso compounds found in the ATNC in beer on the account of knowledge about changes of their content and process of degradation during UV irradiation. In order to find the differences between degradation processes of ATNC, N-nitrosoaminoacids and NDMA during exposure to UV light, the decomposition of the ATNC originally present in beer and the decomposition of selected non-volatile nitrosamines added in a model beer were studied. The determination of selected non-volatile nitrosamines and N-nitrosoamino acids N-nitrosoproline (NPRO) and N-nitrososarcosine (NSAR) was accomplished using a slightly modified gas chromatographic method based on the chemiluminescence detection of the methyl-esters with a thermal energy analyzer (TEA) detector The content of volatile N-nitrosamines was also determined by using the connection GC-TEA. For the determination of the ATNC content, the method Walters et al. was applied.Contrary to volatile N-nitrosamines, about mechanism of decomposion of apparent total N-nitroso compounds and non-volatile nitrosamines e.g. N-nitrosoaminoacids in beer is known only a little. In the first part of this article are therefore given the basic information about their incidence, mechanism of arrising and method of estimation in beer and other foodstuff. The second part of this article is dedicated to the study of the efect of UV irradiation on the ATNC and their some components N-nitrosoaminoacids nitrososarkosine (NSAR), nitrosoproline (NPRO and the main representative of volatile N-nitrosamines N-nitrosodimethylamine (NDMA) in beer. The purpose of this study was to assign previously unknown contents of selected nitroso compounds found in the ATNC in beer on the account of knowledge about changes of their content and process of degradation during UV irradiation. In order to find the differences between degradation processes of ATNC, N-nitrosoaminoacids and NDMA during exposure to UV light, the decomposition of the ATNC originally present in beer and the decomposition of selected non-volatile nitrosamines added in a model beer were studied. The determination of selected non-volatile nitrosamines and N-nitrosoamino acids N-nitrosoproline (NPRO) and N-nitrososarcosine (NSAR) was accomplished using a slightly modified gas chromatographic method based on the chemiluminescence detection of the methyl-esters with a thermal energy analyzer (TEA) detector The content of volatile N-nitrosamines was also determined by using the connection GC-TEA. For the determination of the ATNC content, the method Walters et al. was applied.