Chemical-analytical data were presented illustrating that the mainstream smoke of tobacco products contains traces of volatile N-nitrosamines. The quantity of volatile nitrosamines in the sidestream smoke of cigarettes and cigars exceeds that in the mainstream smoke by at least a factor of 10. This observation led to model studies and analysis of air in bar cars of trains, in a local bar and other indoor atmospheres polluted by tobacco smoke. The results showed that, during one hour in a smoke-polluted indoor environment, one may inhale volatile nitrosamines in quantities equal to those in the mainstream smoke of 0.5-30 cigarettes. It is emphasized that there are, at present, no epidemiological data linking human respiratory cancers to volatile nitrosamines.