The blood pressure, body weight, mean 24 hour urinary electrolyte excretion, and plasma renin activity in offspring whose parents both belonged to the top third of the distribution of blood pressure in their 5-year age-group were compared with those in offspring whose parents belonged to the bottom third. Altogether 116 offspring, aged 10-43 years, took part in the study. Systolic pressure was higher in the offspring with a family history of high blood pressure, but there was no difference in 24-h urinary electrolyte excretion or plasma renin activity. The study had a power of over 80% to detect a 20 mmol difference in sodium excretion, and it provides evidence against the hypothesis that hypertensives have an avidity for sodium.