Background : Carbon monoxide is a colorless, tasteless and odorless gas which is one of the main pollutants considered as a major air pollutant by Environment Protection Agency (EPA). Its side effects on behavioral performance, central nervous system, visual acuity, cardiac and pulmonary functional changes are developed in case of maximum 8-hour concentration of greater than 9ppm. Headaches, fatigue, drowsiness, coma and finally death are known as other side effects. The present study was conducted to determine the concentration of this dangerous gas in Kashan city.

Materials and methods : This descriptive study was performed to measure Co in Kashan in 2000. To meet this demand, Kashan was divided in eight regions and Co was measured in 64 congested and 64 residential areas by Co-Detector.

Results : Results have indicated that residential areas are free of Co but congested areas have shown to be highly polluted.

Conclusion : Bear in mind the dangerous side effects of CO, sources of air pollution in congested areas, (transportation) must be equipped with control devices. Meanwhile, interventions in order to reduce traffic can be helpful.