The International cooperative 'Cardiovascular Diseases and Alimentary Comparison Study' (CARDIAC Study) was designed to study the relationship of dietary factors to blood pressure (BP) and other major cardiovascular diseases (CVD) in widely different populations of both industrialized and developing countries. The primary aim of the research was to test specific hypotheses linking the intake of certain dietary constituents, e.g., sodium (Na), potassium (K), calcium (Ca) and protein, to BP ('Core' Study); in some centers the relationship between dietary factors and mortality from CVD was also examined ('Complete' Study). The final aim of this multicenter research was to contribute to the scientific information base required to guide the formulation of dietary goals for the primary prevention of major CVD. Forty centers in 20 countries are now participating in the CARDIAC Study. From each population 100 males and 100 females aged 50-54 years were selected randomly for BP measurement by an automated system, 24-hour urine collection by aliquot cups, blood sampling etc. according to CARDIAC protocol; and all samples were analyzed by the WHO Collaborating Center (Izumo) by standardized methods. Although studies are now in progress, surveys in China, Tanzania, USSR and Japan suggest the importance of Na and protein intakes, and all data so far obtained of systolic and diastolic BP, urinary Na and K excretions, serum cholesterol levels, etc. show wide distribution in different populations, so that dietary factors of CVD will be analyzed in more detail when the analyses of total samples are completed.