Anti-endomysial antibodies assayed by indirect immunofluorescence presently represent the most advanced in vitro method for diagnosing coeliac disease. While testing the serum of patients affected by coeliac disease for anti-endomysial antibodies, we noticed in some samples the presence of anti-smooth muscle antibodies. This led us to the hypothesis that anti-smooth muscle antibodies might mask the presence of anti-endomysial antibodies. The aim of our research was to develop a method that could confirm our hypothesis. Here we show that the AEA response can be effectively unmasked by increasingly diluting anti-smooth muscle antibodies-positive serum.