The contributions of age and anthropometric, biochemical and socio-economic variables to blood pressure variation in the population of Karkar Island, Papua New Guinea are examined. Blood pressure does not change with age in males; in females there is a decline from ages 21 to 40 and an increase (in systolic pressure) thereafter. Body weight and skinfold thicknesses decline with age in females; arm circumferences decline in both sexes. There were no age effects on serum cholesterol or serum sodium. Variation in ponderal index and subcutaneous fat contribute to variation in blood pressure. The correlations of blood pressure with physique are more important in males and the particular variables concerned suggest a nutritional basis. The socio-economic variables examined showed little variation and this was not associated with variation in blood pressure.