Background: Results of arterial BLOOD gas analysis can be biased by pre-analytical factors, such as time interval before analysis, temperature during storage and syringe type.Objectives: To investigate the effects of samples storage temperature and time delay on BLOOD gases, BICARBONATE and PH results in human arterial BLOOD samples.Patients and Methods: 2.5 mL arterial BLOOD samples were drawn from 45 patients via an indwelling Intraarterial catheter. Each sample was divided into five equal samples and stored in multipurpose tuberculin plastic syringes. BLOOD gas analysis was performed on one of five samples as soon as possible. Four other samples were divided into two groups stored at 22oC and 0oC. BLOOD gas analyses were repeated at 30 and 60 minutes after sampling.Results: PaO2 of the samples stored at 0oC was increased significantly after 60 minutes (P=0.007). The PaCO2 of the samples kept for 30 and 60 minutes at 22oC was significantly higher than primary result (P=0.04, P<0.001). In samples stored at 22oC, pH decreased significantly after 30 and 60 minutes (P=0.017, P=0.001). There were no significant differences in other results of samples stored at 0oC or 22oC after 30 or 60 minutes.Conclusions: In samples stored in plastic syringes, overestimation of PaO2 levels should be noted if samples cooled before analysis. In samples stored in plastic syringes, it is not necessary to store samples in iced water when analysis delayed up to one hour.