Much work has been carried out on N-nitroso compounds but their role in human pathology has still to be elucidated. We cannot extrapolate experimental data to the human situation but we do have indirect evidence that nitroso compounds can be carcinogens in man. Although some nitrosamines are organ-specific, the nitroso group induces the development of many different types of cancer in animals It is probable that the same phenomenon occurs in human pathology, and we cannot therefore expect to have special case reports on their carcinogenicity in man. Therefore, an alternative approach to the study of the role of nitrosamines in human pathology would be to establish a correlation between cancer morbidity in some regions and amounts of N-nitroso compounds in the environment. In view of the complexity of the problem of in vivo nitrosamine formation, it is more realistic nowadays to measure exogenous nitrosamines. Many laboratories are currently engaged on studies on N-nitroso compounds, although systematic information on their presence in the environment is scant. Furthermore, the data acquired by different laboratories has been obtained using a variety of methods for sampling, storage, clean-up and identification and estimation, with the result that it is not known to what extent these results are comparable.Therefore, the standardization and determination of comparability of methods for the identification of N-nitroso compounds is the first step towards their quantitation in the environment. Adequate methods are now available for the determination of volatile nitrosamines, down to the mug/dg level, but methods for non-volatile nitrosamines are still in the development stages. In order to avail all interested laboratories of information on analytical methods for volatile nitrosamines, IARC's analytical chemistry laboratory has organized a three part collaborative study using samples of canned luncheon meat. The results of this study were encouraging, and the European Sub-Committee for the Guidance of Collaborative Studies, at its last meeting, recommended that such studies be continued and extendedto include non-volatile nitrosamines. In parallel with the perfection of analytical techniques, IARC has initiated studies on the measurement of volatile nitrosamines in the environment in conjuction with the epidemiological studies on oesophageal cancer at present being carried out. The data collected up to now is far from being complete but it is important in that it represents the first step towards the evaluation of the risk to health of N-nitroso compounds, which constitute a part of the total carcinogenic load in the human environment.