The longitudinal relation between blood pressure changes and migration experience has been studied in a cohort of 654 adult Tokelauans through three survey periods between 1968 and 1982. Migration from a subsistence life-style on a Pacific atoll to an urbanized Western life-style in New Zealand is associated with increases in body mass in both men and women. Both the systolic and diastolic blood pressures of migrant men are significantly higher than would be expected in this cohort on the basis of age when compared with the nonmigrants. This is consistent with a rise around the time of migration to a level which is then maintained, with the diastolic pressures taking longer than the systolic pressures to respond to the migration stimuli. Most of this rise in blood pressure may be attributed to weight gain, but a significant part of the diastolic pressure excess remains unexplained. This pattern is not exhibited by the women, which may be a reflection of the sex roles in this Polynesian society. These findings indicate a need for new immigrants to be encouraged not to gain weight when confronted with new dietary choices.