Fatal entrapments of Australian bushfire fighters have led to suggestions that carbon monoxide (CO) poisoning could have contributed to these accidents by impairing the fire fighters' judgement. Carboxyhemoglobin saturation (COHb%) levels were assessed from alveolar CO levels in 24 fire fighters working with handtools and in 12 accompanying scientific observers, before and after fire fighting (duration 37–187 min) on 15 experimental bushfires. Carboxyhemoglobin levels increased on average by 0.7% per hour in the fire fighters and by 0.3% per hour in the observers. Nonsmoking fire fighters had lower COHb% after fires than the smokers had before fires. Estimates of environmental CO concentrations (including cigarette smoke) during the fires averaged 31 parts per million (ppm) for the smokers, 17 ppm for the nonsmoking crew members, and 11 ppm for the observers, none of whom smoked. The highest estimates of environmental CO arising solely from bushfire smoke were 40 to 50 ppm. Smokers were exposed to as much CO from their cigarettes as from bushfire smoke. Carboxyhemoglobin levels at the end of 8-hr fire fighting shifts, predicted from these levels of environmental CO, averaged about 5% (maximum 11%) in smokers and about 3% (maximum 7%) in nonsmokers. Acute levels of COHB% of this degree are not considered to have significant effects on health or performance. These results indicate that bushfire fighters are generally unlikely to experience hazardous levels of CO exposure.