['The measurement of expired carbon monoxide (CO) is a direct and non-invasive method for the detection of exposure to CO.', 'Our aim was to investigate the impact ofatmospheric pollution and smoking on expired CO in kiosk workers in Thessaloniki, Greece.', 'Twenty kiosks were selected in the commercial centre of city. The workers were all men aged 30.5 +/- 5.5 years. Measurements of expired CO and environmental CO were carried out twice per day, during two different seasons of the year, summer and winter. Expired CO was measured via a MicroCOMeter equipped with a fuel cell type electrochemical sensor. The CO levels in ambient air were determined using the method of Non-Dispersive Infra-Red analysis.', 'Ambient CO levels were 2.11 +/- 0.64 ppm at h. 17:00 and 3.64 +/- 1.45 at h. 21:00 in winter and 1.26 +/- 0.17 ppm at h. 17:00 and 1.73 +/- 0.22 at h. 21:00 in summer. Expired CO in non-smokers was 3.2 +/- 2.7 ppm at h. 17:00 and 4.2 +/- 3.2 at h. 21:00 in winter and 1.3 +/- 1 ppm at h. 17:00 and 2.2 +/- 1.4 at h. 21:00 in summer. In smokers it was +/- 5.2 ppm at h. 17:00 and 13.9 +/- 7.5 at h. 21:00 in winter and 10 +/- 4.8 ppm at h. 17:00 and 18 +/- 7 at h. 21:00 in summer. All these differences were statistically significant. The concentrations of expired CO were significantly correlated with the number of the cigarettes smoked.'] Do smoking and pollution cause an increase in expired carbon monoxide in kiosk workers?