The determination of air nicotine content is very important to estimate the amount of this toxic which is inhaled by the non-smokers. In this study, a process of its evaluation, is expanded, that presents good analytical performances. This process was applied to various determinations : in an office, while 20 cigarettes were burning, and fifteen hours after, in the same office non-ventilated, in a bar, and in an university lecture hall. These experiences showed up that the nicotine distribution in air was not homogeneous, and brought the questions of its adsorption and of its persistence in the atmosphere. Another study was realized by sampling the air near some non-smokers during two periods of 24 hours. According to the exposure conditions, the nicotine air levels were between 0 and 41 µg . m^-3, and corresponded to 0 to 0,50 "cigarette-equivalent". These low levels have to be confirmed by a determination of nicotine in biological fluids, which is necessary to conclude about the inhalation of ETS by the non-smokers.