Firemen threat during fire burning of chemical substances indicated presence of carbon monoxide (CO) in all cases. Carbon monoxide causes death of fire. Inhaled through respiratory system, links with hemoglobin, thus blocking transport and distribution of oxygen in the body. This leads to tissue anoxia, which is a direct threat to firefighters’ life. The purpose of this study was to assess the exposure to carbon monoxide of participating firefighters extinguishing fire. Estimation of carbon monoxide quantity absorbed by firefighters was isolated in a group of 40 firefighters from Fire Extinguishing and Rescue Unit of State Fire in Nysa. The study was conducted by measuring carbon monoxide in exhaled air. For measurement of carbon monoxide concentration in exhaled air Micro CO meter was used. Results were demonstrated separately for nonsmokers (n425) and smokers (n415). Mean COHb[%] levels in nonsmokers, measured prior the rescue action was 0,39±0,3% and increased statistically significant after the action to 0,61±0,34%, while in the group smokers, this level was 2,17±0,64% before the action and increased insignificantly after the action to 2,3350,63%. The average COHb level in the same groups before and after exercise, was respectively: for nonsmokers prior to exercise was 0,48±0,28% and after exercise decreased statistically significant to 0,30±0,27%. In the group of smokers before exercise was 2,23±0,61% and decreased statistically significant up to 1,54±0,71%. It was no difference between the group of age and time of employment.