369 E. coli strains that are agglutinated in A or B anti E. coli enteroinvasive (EIEC) polyvalent sera and inducing no keratoconjunctivitis in the guinea pig's eye have been selected. The biochemical reactions of E. coli strains that can be agglutinated in A or B EIEC polyvalent sera occupy an intermediary position between those of Shigella genus and the classical features of Escherichia, i.e.; 87% are motile bacteria, 88%--ferment lactose, 81% form acid from sodium mucate and lysine is not decarboxylated by 87% of the strains. As for the antigenic behaviour with 15 out of the 16 sera employed, the strains under consideration have agglutinated by slide test in one or several sera, with varying intensities. None of the strains agglutinated on slide in the O164 antiserum. Subsequently, agglutinations have been performed in tubes only with the strains that agglutinated on the slide with a +3 or +4 intensity. Out of the 369 strains under consideration only 25 have agglutinated in the tube, all the false positive reactions representing 6.7%. The data presented lead to the conclusion that such strains that have been isolated from ill or healthy patients cannot be considered as pathogenic diarrhoea agents, the differentiation from the invasive strains (in the absence of the guinea pig for the pathogenicity test) cannot be made on the basis of the biochemical reactions, but only by means of a set of monovalent sera and by performing the tube agglutination tests.(ABSTRACT TRUNCATED AT 250 WORDS)