Four fractions, fraction A,B, C, and D, were isolated from the aqueous extract of wheat flour on a Sephadex G-75 column. It was found that the repeated gel-filtrated fraction A reacts as an antigen with the sera of coeliac patients. On the basis of its molecular weight and amino acid compositions, it is gliadin. Each of the 28 coeliac patients had heat-stable precipitating antibody and higher than normal IgE levels were found in the sera of only three individuals. Specific antigliadin IgE in low quantity was found in only one case. The sera reacting with antigens in high titres were absorbed by anti-IgG and anti-IgA whereupon the antibody level considerably decreased. The main circulating antibody of the patients was IgG.