Celiac disease (CD) is a genetically based chronic inflammatory disorder of the small bowel induced by the dietary gluten and possibly other environmental cofactors. The objective of this study was to investigate the relation of adenosine deaminase (ADA), a cytoplasmic enzyme involved in the catabolism of purine bases, as an index of altered immune response, with adult CD patients. ADA has been shown to increase in several inflammatory conditions, but there is no literature data indicating an alteration in CD. Serum levels of ADA were investigated in newly diagnosed 20 CD patients. ADA levels were compared in patients with CD and in healthy controls. Correlation analysis was also performed between ADA and other serum markers of CD (anti-gliadin and antiendomysial antibodies) Mean serum ADA levels were significantly elevated in CD patients compared with control group. ROC curve analysis suggested that the optimum ADA level cut-off point for CD was 12.27U/l. At a cut-off value of 12.27U/l, the sensitivity was 80% and specificity was 100%. There was no statistically significant correlation between ADA and anti-gliadin and anti-endomisium antibodies. Serum ADA levels elevated significantly in CD patients, suggesting a partial role in activated T-cell response in the disease pathophysiology. ADA can be used as a supportive diagnostic marker in patients with CD. © 2010 Wiley-Liss, Inc.