A total of 107 venous blood samples were obtained from blood donors in Bahrain for carboxyhemoglobin (COHb) analysis. The donors were categorized according to their sex, smoking habits, occupation, place of work (indoor or outdoor), and residential areThe mean COHb levels were significantly higher in smokers (4.8%) than nonsmoking (1.5%). The mean COHb levels were higher in smoking, outdoor working donors (4.98%) and nonsmoking outdoor working donors (2.29%) than smoking indoor working donors (3.07%) and nonsmoking indoor working donors (1.04%). Other factors, such as sex and residential area did not influence COHb concentrations. The results indicate a possible influence of the levels of environmental carbon monoxide on the COHb in the blood of the Bahraini population.