In spite of intensified antitobacco campaigns and decrease in social acceptance for smoking it is still an important issue. In prevention there is a need to make smokers and non-smoking people aware of a level of exposure to tobacco smoke. One of the objective methods to evaluate this exposition is to measure a concentration of the carbon monoxide in exhaled air. The aim of our study was to evaluate the indication of carbon monoxide in exhaled air. The research was based on examination of 67 patients admitted to admission room in SP CSK, Warsaw. The level of carbon monoxide was measured with Smokerlyzer device in 56 cases (34 women, 22 men). Everyone in this group answered questions concerning a reason of admission to hospital, concomitant diseases, and addiction to smoking and ways of fight against the addiction as far as smokers are concerned. Current smokers answered also questions about their attitude to smoking and filled in Fagerström and Schneider tests. In a group of 67 patients 11 were not able to proceed the test with Smokerlyzer, 5 (45.5%) due to dyspnea, 4 (36.4%) due to lack of a verbal contact. In the group of 56 investigated patients 20 (35.7%) have never smoked, 32 (57.1%) were ex-smokers and 4 (7.1%) were current smokers. 3 (75%) of the smokers have tried to give up smoking 3 times on average. In the Fagerström test their mean came to 3.5 points, what indicates a low level of addiction. The Schneider test averaged out 8 points, what indicates a good motivation to give up smoking. The average of concentration of carbon monoxide in exhaled air came to 8 ppm (1.87% Hb) in this group. In the group of non-smoking patients the level of carbon monoxide came to 1.4 ppm (0.67%Hb). In the group of nonsmoking patients exposed to the tobacco smoke, the level of carbon monoxide came to 3 ppm (1.15%), but the difference was not statistically significant (p > 0.05). The increased CO level in exhaled air is usually caused by smoking cigarettes and exposure to ETS. All the smokers acknowledged the addiction. Routine use of Smokerlyzer in the admission room is limited, mainly by the dyspnea. Despite the practicality of CO level measurement, taking medical history of smoking is still the most important.