Diarrhoea caused by intestinal infections is the commonest symptom affecting travellers particularly those from developed countries with temperate climates who are visiting less advanced countries in tropical and subtropical parts of the world. It can be troublesome, embarrassing and sometimes incapacitating and has spoiled many holidays.

The infections are almost invariably contracted from food or water although the primary source is usually man, frequently a food handler who is a faecal carrier of one or more pathogenic organisms and whose personal hygiene is inadequate. In many tropical countries human faeces (‘night soil’) is used to fertilise crops especially vegetables such as lettuce and if these are eaten uncooked or unwashed intestinal infection may result.

Infective diarrhoea in travellers may be caused by bacteria, viruses or certain protozoal organisms. Bacterial aetiological agents include Salmonellae, Shigellae, Vibrio cholerae and also certain strains of Escherichia coli which are capable of producing enterotoxins. These enterotoxins are potent causes of diarrhoea in travellers. Recently recognised as a bacterial cause of intestinal infection in travellers are campylobacter species. The protozoa which cause travellers' diarrhoea are Entamoeba histolytica and Giardia lamblia, the latter organisms being a common cause of chronic diarrhoea in recent travellers. A number of recently recognised viruses have been associated with diarrhoea in travellers, the most notable being rotaviruses.

The above micro-organism;, cause disease in the intestinal tract by different pathogenic mechanisms which are described in this paper.

The prevention of travellers' diarrhoea, especially the use of chemoprophylaxis, is a controversial topic which is discussed.

It has been estimated that approaching one thousand million people will travel annually on commercial airlines by the end of the present decade. Many will be transported to tropical and subtropical countries and it is, therefore, an opportune time to consider the present topic.