The incidence rate of hepatitis A is 3(-6)/1000 per month of stay in a developing country in unprotected travellers. Tramps and other persons feeding themselves under bad hygienic conditions have a rate of 20/1000. In many industrialized countries, persons below the age of 50 years have a seroprevalence rate of anti-HAV < 20%. Hepatitis A morbidity and mortality rates in travellers are far greater than those of any other vaccine-preventable infection in travellers, with the exception that hepatitis B shows a slightly greater mortality rate in expatriates. Future studies will determine the role of hepatitis C and E. Typhoid fever shows an incidence rate of 0.3/1000 in foreigners on the Indian subcontinent, and in many parts of North and West Africa, excluding Tunisia; in other parts of the Third World it is tenfold lower. In poliomyelitis, tetanus, diphtheria, cholera, rabies and Japanese encephalitis the incidence rate is < or = 0.002/1000.