The physiological and nutritional status of adult Tongans in rural (Uiha, 50 males and 58 females) and urbanized (Kolofo-ou, 77 males and 71 females) areas were surveyed in 1977 and 1979, respectively. Adult Tongans of both sexes in the two districts had considerably large physiques. Being different from the obesity found in peoples of industrialized countries, the obese state of adult Tongans was associated with large muscularity, low incidence of glucosuria, ECG abnormalities and hypertension, and normal plasma cholesterol levels. However, modernization has started to have an influence upon the health of adult Tongans; relatively high levels in parameters relating to obesity as well as higher incidence of hypertension were observed in adult Tongans in Kolofo-ou as compared to adult Uiha islanders.