The systolic and diastolic blood pressure was measured in a nationwide probability sample of persons of both sexes and the two largest racial groups in the United States. Respondents were aged 18–79 years and useable blood pressure data were available for 6,546 of 7,710 (85%) of the total sample. The data are presented in percentiles for Caucasians and Negroes separately by age and sex; age and sex specific means and standard deviations are also presented by racial group. Systolic and diastolic pressure show in general the expected increase with age, and the distribution is skewed. Attention is drawn to the fact that while for systolic pressure there is an increase with age of the lower percentiles in women of both racial groups, there is no such age trend in these percentiles in man of either racial group. Patterns for diastolic pressure are similar, though less clear-cut.