Nitrogen oxides (NO x), especially nitrogen dioxide (NO 2), are among the most hazardous forms of air pollution. Tobacco smoke is a main indoor source of NO x, but little information is available about their concentrations in second-hand smoke (SHS), particularly in small indoors. This study presents data of NO x and its main components nitric oxide (NO) and NO 2 in SHS emitted by ten different cigarette brands measured in a closed test chamber with a volume of 2.88 m 3, similar to the volume of vehicle cabins. The results show substantial increases in NO x concentrations when smoking only one cigarette. The NO 2 mean concentrations ranged between 105 and 293 µg/m 3, the NO 2 peak concentrations between 126 and 357 µg/m 3. That means the one-hour mean guideline of 200 µg/m 3 for NO 2 of the World Health Organization was exceeded up to 47%, respectively 79%. The measured NO 2 values show positive correlations with the values for tar, nicotine, and carbon monoxide stated by the cigarette manufacturers. This study provides NO 2 concentrations in SHS at health hazard levels. These data give rise to the necessity of health authorities' measures to inform about and caution against NO x exposure by smoking in indoor rooms.