Shiga-like toxin presence, in 20 E. coli strains, etiological agents of diarrheal diseases, is studied by preparing extracts at +4 degrees C, in the presence of chloroform and by i.v. inoculation in mice. In 4 out of 20 strains, Shiga-like toxin in high titres was identified. Most of the strains presented an inconstant and variable production of Shiga-like toxin in comparison with Shigella dysenteriae type 1 (Shiga) reference strain. The authors also confirm the existence of Shiga-like toxin under 2 forms (neutralizable with Shiga antitoxic serum and non-neutralizable). The importance of the obtained results is further discussed from the point of view of pathogeny and diagnosis of the infections produced by these germs.