Enterotoxigenic Escherichia coli (ETEC) causes an acute cholera‐like diarrhoea in both humans and animals. We describe a new pilus termed longus produced by ETEC, which can extend for over 20 microns from the cell surface. Longus is composed of a repeating subunit of 22 kDa and its NH₂‐terminal amino acid sequence revealed homology with the toxin‐coregulated pilus of Vibrio cholerae, the bundle‐forming pilus of enteropathogenic E. coli and type IV pilins of some Gram‐negative bacterial pathogens. The longus structural gene (IgA) is encoded in a large plasmid and was cloned in a 5 kb fragment, which proved to be sufficient for pilus production and assembly in E. coli K‐12. The presence of IngA was restricted to human ETEC strains. In contrast to other ETEC pili, IngA was widely distributed among ETEC strains independent of their geographical origin, serotype, toxin production, or other pili antigens expressed. Longus is a new member of the type IV pili family, which may represent a highly conserved intestinal colonization factor of ETEC. Common antigenic determinants exist among longus and their pilin subunits, produced by heterologous ETEC. Longus could be significant in the immuno‐prophylaxis of diarrhoeal disease caused by ETEC, especially against those strains in which no colonization factors have been identified and that produce heat‐stable toxin only.