Among 391 P. shigelloides strains, 330 were typable and found to belong to 43 O serovars. The most frequent O serovars were O17 (23%), O32 (7%), O12 (4.5%) and O5, O18 and O44 (3.8% each). The majority of the serovars represented, with almost 300 strains, were sporadically found in very distant countries of three continents (Europe, Asia, America), whereas only one serovar (O68) was isolated three times in one single district of South Bohemia (Ceské Budéjovice). It suggests that such an incidence of plesiomonads is only seemingly sporadic and that there must be many strains which are not detected owing to the imperfect cultivation methods used so far.