The hypothesis that regular jogging diminishes blood carboxyhemoglobin levels was tested, 63 smokers were chosen, when 30 of them regular joggers for 3 years and 33 of them sedentary non-joggers. Blood samples were taken and carbon monoxide levels measured by a gas chromatograph. Results showed that smoking joggers had significantly lower carbon monoxide levels than smoking non-joggers, with values of the former comparable to non-smokers.