The high Na/low K environment of modem society is related to the genesis of hypertension and stroke. There is prior evidence of racial, geographical, and social class differences in Na and K intake and blood pressure. Baseline data from the Treatment of Mild Hypertension Study (TOMHS) was used to assess urinary Na and K excretion profiles by race, clinic geographic area, and education. Participants were adult black and white hypertensive patients from the Birmingham, Alabama, and Chicago, Illinois, area. Level of education was categorized as: less than college graduate and college graduate or more. Two overnight urine samples were collected and analyzed for Na and K at entry from 154 blacks and 281 whites. The urinary Na:K ratio was significantly higher in both blacks (5.1 v 3.8, P < .001) and whites (4.1 v 3.4, P < .005) in Birmingham compared with Chicago. This was primarily due to the lower excretion of urinary K in blacks (12.8 v 16.9 mmol/8 h, P < .01) and whites (14.0 v 16.5 mmol/8 h, P < .01). The highest urinary Na:K ratio was observed in blacks in Birmingham with lower education level; urinary Na excretion was high in blacks with a lower education level in both cities. No such differences were seen in whites. Although TOMHS was not population-based, these findings suggest the possibility that potassium intake among persons with stage 1 hypertension is related to geographic area in both blacks and whites, and sodium intake is inversely related to education level in blacks.