The relationship of parental history of high blood pressure (HBP) to blood pressure (BP) was estimated in three Japanese population samples, totalling 591 men and women aged 20-59 years, from the INTERSALT study. Parental history of HBP was defined as reported HBP by their father and/or mother. With adjustment for antihypertensive medication, body mass index, alcohol intake, and Na/K ratio in 24-h urine, for participants with a parental history of HBP compared to those without a history, BP was higher for three to four age-sex strata, both for systolic and diastolic pressure (SBP, DBP), by 3.3 to 6.8 and 2.7 to 5.5 mm Hg respectively, with four of these six positive associations statistically significant. This finding was stronger for persons aged 40-59 than for those aged 20-39. These data support the judgment that for persons with a parental history of HBP, BP is apt to increase more with age due to combined effects of genetic and environmental factors. Such people especially need to control their lifestyles carefully, including to maintain an optimal intake of salt (eg, <70 mmol/day) and a high potassium intake, to avoid high alcohol consumption, and keep weight moderate, for the prevention of hypertension.