Background: It's possible to view tobacco usage and smoking as a scourge on a healthy society. Individuals who are in close proximity to smokers breathe in their smoke and are referred to as "secondary smokers" or "passive smokers." The present study was conducted to assess breath carbon monoxide level of non- smokers. Materials & Methods:50 maleswere divided into 2 groups. Group I consisted of 25 non-smokers exposed to environmental tobacco smoke (ETS) and group II consisted of 25 non-smokers not exposed to ETS. All subjects underwent clinical examination. Breath CO levels of both the groups were measured by the Mini Smokelyzer. Results: Age group 21-30 years had 7 subjects in group I and 8 in group II, 31-40 years had 13 in group I and 11 in group II and 41-50 years had 5 in group I and 6 in group II. The difference was significant (P< 0.05). Breath CO level 0-6 (ppm) was seen in 2 and 16, 7-10 (ppm) in 17 and 9 and >10 (ppm) in 6 subjects in group I and II respectively. The difference was significant (P< 0.05). Conclusion: With respect to non-smokers In addition to other negative effects of smoking, respiratory illnesses are more common in passive smokers. Smokers ought to be aware of the negative effects smoking has on other people as well as on themselves and give up smoking in public areas, hotels, restaurants, and pubs.