Influence of aging on plasma renin activity was evaluated in healthy normotensive subjects (age range $21sim63$ years, 413 males) devoid of cardiorenal or endocrinological problems. The age-related decrease of plasma renin activity in the subjects between $21sim28$ years group and $36sim42$ years group was slight, but over the 43 years groups was significantly different. The age-related suppression of plasma renin activity was much more smooth and continuous all over the age ranges evaluated. The sexual difference in plasma renin activity was noticed between the subjects of 22 years old group(34 males) and 19 years grop(34 females) (p<0.003). The data suggest that the age-related suppression of plasma renin activity appeared in healthy normotensive subjects should be considered in the case of evaluation of low renin essential hypertension.