1. Platelets have been used as a model of sympathetic neurons to study the storage of noradrenaline in normotensive individuals belonging to families with essential hypertension for at least two generations.
2. The initial efflux rate (k) of noradrenaline was determined in 44 young relatives (mean age 29.2 years), in 18 middle-aged relatives (mean age 46.7 years) and in 31 young controls with no known family history of essential hypertension (mean age 29.8 years). From the groups of relatives all those with definite hypertension had been excluded a priori.
3. k was significantly higher in the young relatives (22.7 ± 7.9) than in the middle-aged relatives (17.7 ± 6.4) and in the controls (15.6 ± 5.1). Of the relatives 27.3% had higher k values than any of the controls. A significant correlation was found between k and diastolic blood pressure in controls but not in young relatives.