Celiac disease (CD) is mediated by IgA antibodies to wheat gliadins and tissue transglutaminase (tTG). As tTG is homologous to microbial transglutaminase (mTG) used to improve foodstuff quality, it could elicit the immune response of celiac patients. This study evaluated the reactivity of IgA of celiac patients to prolamins of wheat and gluten-free (maize and rice flours) breads mTG-treated or not. Prolamins extracted from wheat and gluten-free breads were analyzed by ELISA and immunodetected on membranes with individual or pooled sera from nine celiac patients recently diagnosed. Sera pool IgA titers were higher against prolamins of mTG-treated wheat or gluten-free breads than against mTG-untreated, mainly due to two individual patients' sera. The electrophoretic pattern of gluten-free bread prolamins was changed by the mTG treatment, and a new 31000 band originated in maize was recognized by three CD patients' IgA.