Studies on the health effects of diasters show that epidemiological indices can be of value in planning preventive and relief measures and in evaluating their effectiveness. Mortality rates naturally vary considerably, but in earthquakes, the number of deaths/100 houses destroyed can give an indication of the adequacy of building techniques. Age-specific mortality rates can help to identify particularly vulnerable groups and perhaps indicate what form of education would be valuable. Except in earthquakes, the number of casualties after a disaster is usually low in relation to the number of deaths, and study of the distribution and types of lesions would help in planning the amounts and types of relief supplies and personnel required. Diasters also affect the general level of morbidity in a district because of interruption of normal health care services or of spraying or other disease control measures. Mental health and nutrition following diasters are particular problems that require further investigation. Study of all these features of disasters is handicapped by a lack of data, particularly concerning the health situation immediately after the impact. The provision of surveillance teams in diaster-prone areas would appear to be a field in which international cooperation could yield immense benefits.