Background: In recent years, the need for more accurate determination of trace elements has been increasing in biological research. This study aimed to compare the serum-Selenium level in patients with Down's syndrome (DS) and the healthy control group.

Materials and Methods: In this study, the quality control samples were determined using a graphite furnace atomic absorption spectroscopy (GF-AAS) in both the patients and control group.

Results: Down syndrome patients showed lower level of selenium in serum (74.2 ± 1.47 µg L-1) compared to that of the healthy control group (84.7 ± 1.63 µg L-1). The mean difference of both groups (t= 3.15) was statistically significant (P<0.001) suggesting that the patients has a decreased serum-Selenium level compared to the healthy group.

Conclusion: Results of this study indicate that selenium plays an important role in the pathogenesis of DS patients. The calibration curve was linear in a concentration range of 5-40 µg L-1 (R2 > 0.999) with the detection limit of 0.6 µg L-1 level. An acceptable reproducibility (< 3.50%) and good recoveries between 95-98 % were obtained. Reference material was used for method validation.