With the indirect immunofluorescence technique using sections of colon from guenon and rat, sera from patients with ulcerative colitis yielded positive staining of goblet cells. Eight sera, thus defined positive, two negative, and five from hospital controls, were applied to agar preparations of 12 different E. coli strains, normally found in human bacterial diseases and E. coli 0 14. With E. coli 0 group antigens, 2, 8 and 14 positive fluorescence reactions were regularly found in sera where positive immunofluorescence reaction aginst colon antigen could be demonstrated, indicating that antigen(s) from colon mucosa shares antigenic determinant(s) with some E. coli bacteria or bacterial components.