Background: Endomysium antibodies (EMA) do not detect minor dietary transgressions in patients with celiac disease. Aim: To compare the sensitivity and specificity of tissue transglutaminase antibodies (tTGA) and endomysium antibodies (EMA) in biopsy proven celiac patients at the time of diagnosis and during gluten free diet (GFD). Patients and methods: One hundred fifty three subjects were studied: a) 30 healthy controls; b) 9 cases with cow's milk allergy; c) 24 celiac patients at time of diagnosis; d) 25 celiac patients adhering to the GFD; e) 65 celiac patients with poor/no adhesion to GFD. EMA and tTGA IgA were measured by immunofluorescence and ELISA, respectively. Results: Sensitivity and specificity were 100% and 97.4% for tTGA, respectively. All patients with cow's milk allergy were EMA (-) and 8 of 9 (88.9%) were tTGA (-). In celiac patients not adhering to the GFD, EMA and tTGA positivity were similar (80% and 81,5%, respectively); 95,4% of the subjects tested positive for at least one of them. All patients adhering to GFD were EMA (-) but tTGA were (+) in 28% of them. Conclusions: EMA and tTGA have similar sensitivity and specificity at the time of diagnosis of celiac disease. Positive tTGA in 28% of patients that adhered strictly to the GFD and whose EMA were negative suggest that tTGA may be helpful in detecting minor dietary transgressions and should be further evaluated (Rev Méd Chile 2003; 131: 25-29)