Dietary data were obtained from 110 adult Polynesians (indigenous Funafutians) during a diabetes epidemiologic survey in Tuvalu. Funafuti (the main island of Tuvalu) was chosen as representative of partly urbanized population that has seen progressive socioeconomic changes in the previous 30 yr. The distribution of calories in the Funafuti diet is almost identical to that reported in the urbanized Micronesian population of Nauru and in Caucasian populations. Prevalence of diabetes was found to be five times higher than that reported in caucasian populations. Similarly, the prevalence of hypertension was 11% (equal to Caucasian figures), whereas hypertension is virtually unknown in traditional-living populations. Prevalence of diabetes, and degree of obesity, is significantly greater in women than in men. It is possible that this Polynesian group may have a genetic susceptibility to diabetes, which may have been unmasked by change from a traditional to western life-style. Marked obesity is now a characteristic of many Polynesian and Micronesian populations, and must rank as a major causative factor for the diabetes and hypertension explosion.