The relationship of renin activity to sex, race (black or white) and age (less than 50 or greater than or equal to 50 years of age) was examined in 236 normal subjects measure yearly for up to 9 years. There were 58 white women (34 less than 50 years, 24 greater than or equal 50 years), 66 white men (30 less than 50 years, 36 greater than or equal to 50 years), 57 black women (34 less than 50 years, 23 greater than or equal to 50 years) and 55 black men (34 less than 50 years, 21 greater than or equal to 50 years). The results showed men had higher mean renin activities than women, whites had higher activities than blacks and those of under 50 years had higher activities than those of over 50 years. However, the sex and race differences primarily occurred as a consequence of a lack of decline in renin activity with age among white men. The relationship with age as a continuous variable was weak (r = -0.21) and no relationship with age was found in 22 subjects with a least 7 years of data. No significant differences in urinary sodium excretion were observed between the groups. These results suggest that renin activity tends to be lower in older subjects and that differences in renin activity related to sex and race, while statistically significant, may not be physiologically important.