Even though enterotoxin-producing Escherichia coli (ETEC) is the most important cause of diarrhoea in developing countries and among travellers, no vaccine for use in humans is yet available. New knowledge about virulence factors and protective antigens of ETEC, however, suggests that development of a useful vaccine may soon become possible. Such a vaccine should be given orally and ideally evoke both anticolonization and antitoxic immune responses in the gut. An oral cholera vaccine, containing a component (B subunit) which crossreacts immunologically with the major, heat-labile enterotoxin (LT) of ETEC, has been shown to afford significant protection against diarrhoea caused by LT-producing ETEC. Promising prototype oral ETEC vaccines combining B subunit toxoid with inactivated ETEC bacteria expressing the most prevalent colonization factor antigens (CFAs) have been developed, and work is in progress to find means for adding to this CFA-toxoid vaccine a component that could also provide immunity against heat-stable enterotoxin.