The present paper summarizes the serotyping scheme of the fish pathogenic bacterium Vibrio anguillarum and defines seven additional O-serogroups. Strains, collected in our laboratories that were nontypable with antisera against the previously defined 16 O-serotypes, were used for generating new antisera and were characterized further by means of LPS profiles, Western blots, and serological reactions. On the basis of the results, it is suggested that the seven new O-serogroups are to be included in the existing serotyping system as serotypes O17-O23. However, the existence of further V. anguillarum strains that were not typable with any of the 23 O-antisera suggested the existence of additional O-serotypes within this species. The relevance of the description of additional O-serotypes for the species V. anguillarum is discussed.