We studied 15 normotensive offspring of hypertensive parents, comparing them with 15 normotensive controls matched for sex, body mass index and age. In the offspring, both parents were hypertensive, while in the controls, neither parent was hypertensive. Blood pressure was measured at rest, during a variety of laboratory stressors (mental arithmetic, mirror drawing test, hand grip and cold pressor test), and was also monitored for 24 h in ambulatory conditions (Spacelabs 5300 M, Richmond, Washington, USA). Resting mean and diastolic blood pressures were higher (P less than 0.05) in the subjects with parental hypertension than in those without. The mean blood pressure rise induced by the laboratory stressors was not significantly greater at any time in the subjects with hypertensive parents compared with controls. Twenty-four-hour systolic and mean blood pressures, however, were significantly higher (P less than 0.05) in the subjects with hypertensive parents than in the controls. Thus the higher office blood pressure shown in the prehypertensive stage by subjects with parental hypertension is not due to hypersensitivity to stress, but represents an early and permanent blood pressure elevation.