An antiserum against the synthetic disaccharide abequose 13 rhamnose (AR), representative ofSalmonellaO‐antigen 8, coupled to bovine serum albumin (BSA) was used for diagnosis ofSalmonellabacteria by indirect immunofluorescence (IFL) and by co‐agglutination (COA) using sensitized protein A‐containing staphylococci. Among the 1150 enteric bacteria tested in IFL, the antiserum correctly identified all 99Salmonellaserogroup C 2 and C 3 bacteria with O‐antigen 8. No fluorescence was seen with 484Salmonellabacteria belonging to other serogroups or 567 non‐Salmonellaenteric bacteria. The anti‐AR‐BSA serum was favourable as compared to a conventionalSalmonellafactor O8 serum as regards both titre and specificity. In the COA test, all 22Salmonellaserogroup C 2 and C 3 strains agglutinated strongly and within seconds, whereas no agglutination could be seen when 93Salmonellabacteria representing other serogroup