Soluble peptidoglycan-polysaccharide complexes (PPC) isolated from feces of a healthy subject shared antigens with 22 out of 40 anaerobic intestinal bacteria and, therefore, these could be considered as flora derived. IgG, IgA and IgM antibodies against PPC were found in sera from healthy subjects, patients with Crohn's disease (CD) and other patients. In sera of CD patients with agglutinating antibodies to 4 anaerobic intestinal bacteria (used as an aid for diagnosis of CD) IgG and IgA levels to PPC were higher than in CD patients without these antibodies.