Objective To investigate the effect of conventional preseratives on the stability of carboxyhemoglobin(HbCO)in the stored blood samples.Methods Blood samples with 30%～40% and 60%～70% of HbCO were established,respectiviely.The samples were stored with the commomly used preseratives including formaldehyde,sodium fluoride,EDTA-Na_2,sodium nitrite,potassium oxalate,heparin sodium,sodium citrate and the mixture of sodium fluoride and sodium citrate(1:3).Saturation of HbCO in the preserved blood samples were determined at 0h,2h,8h,24h,3d,and 7d after treatment with the addictives,respectively.The data were evaluated statistically.Results The stability of HbCO was significantly affected in the formaldehyde and sodium nitrite-treated samples,but no significant effects of the other preseratives on the blood samples were detected.Conclusion The stability of HbCO in the blood samples conserved varies with the type of the preseratives used.The samples taken from cases with suspected death from carbon monoxide poisoning should be kept with proper preseratives.Blood samples preserved with formaldehyde and sodium nitrite are not suitable for HbCO determination.