50 to 70% of diarrheas contracted during travel in hot countries are due to an enterotoxigenic E. coli having the dual acquired ability to adhere to the intestinal epithelium and to produce an enterotoxin. This produces a liquid diarrhea, usually banal for the traveller but which can sometimes be serious in young children of developing nations. The genes coding for the above two characteristics are carried by a plasmid. Other colibacilli, enteropathogenic or entero-invasive, can also cause diarrhea; being liquid in the former case and dysenteriform in the latter. Other bacteria such as the vibrions and perhaps Aeronomonas, can also secrete an enterotoxin. The role of invasive organisms and viruses is briefly discussed. The prophylaxis is fairly illusive and treatment of the mild forms is usually symptomatic.