Vero cytotoxin-producing Escherichia coli (VTEC) are an important cause of disease in man and animals. In addition to the production of VT these strains may possess other properties that are required for full virulence. Examples of some recent molecular studies are reviewed. Use of oligonucleotide probes and the polymerase chain reaction provide methods for the identification and typing of different VT genes. Several VTEC have the ability to cause attaching and effacing lesions of the epithelial microvilli. Hybridization experiments with the eae probe (E. coli attaching and effacing) showed homology with VTEC of human origin of eight different O serogroups. Properties of VTEC from human infections have been compared to strains isolated from animals and foods.