Some 2600 elderly people born between 1913 and 1918 have been enrolled in the Euronut SENECA study. In 12 European countries they were randomly selected from the resident populations of 19 'traditional' towns, mostly with a population size between 10,000 and 30,000 inhabitants. Site characteristics of these towns differ from mainly rural to urban and from lowland to mountainous with a range of temperate climates. In the rural areas work opportunities are primarily agricultural whereas in mixed rural/urban, suburban and urban areas most of the working population are engaged in industry, administration and commerce. The percentage of people over the age of 65 ranged from 8% to 22%. Medical and social facilities for the aged vary widely from site to site.