The Pacific atoll population of Tokelau has been followed since 1968 to assess the health consequences of migration to a western society. The blood pressure of a cohort of 532 adults who were still living in Tokelau in 1976 (nonmigrants) are compared with those of a cohort of 280 adults who had migrated to New Zealand (migrants). Significant differences between migrants and nonmigrants were detected in the rates of change of both systolic and diastolic pressures in men, and in the rates of change of diastolic pressures in women. The age-, body mass, and blood pressure-corrected rates of change were greater in migrants than in nonmigrants, and greater in men than in women. Blood pressures tend to rise 1 mmHg/year faster among male migrants than among male nonmigrants, and about 0.4 mmHg/year faster among female migrants than among female nonmigrants. These findings have clear implications for the health of migrants.