Vero-cytotoxin-producing strains of Escherichia coli (VTEC) were identified by the use of DNA probes in 39% of faecal samples from patients with haemorrhagic colitis in England and Wales. The patients with VTEC were distributed widely and their ages ranged from 2.5 to 86 years (mean 41). 3 patients died, including a child of 2.5 years. 30 of the 32 VTEC strains belonged to serogroup O157. Plating on sorbitol agar for non-fermenters followed by agglutination with a specific O157 antiserum was a useful screening method for O157 VT+ strains. However, it was not as sensitive as the DNA probe technique and did not detect VTEC of other serogroups.