The rate of urinary albumin excretion is an important risk factor for kidney failure, stroke, and cardiovascular disease, perhaps because higher albumin excretion reflects endothelial cell dysfunction. The authors characterized urinary albumin excretion according to blood pressure, diabetes mellitus, and other factors in 2,582 Black and White participants in the Coronary Artery Risk Development in Young Adults (CARDIA) Study who were aged 18-30 years in 1985-1986. Urinary albumin and creatinine concentrations were determined using single untimed samples 10 and 15 years later. The albumin:creatinine ratio was analyzed as a continuous variable and a dichotomous variable (higher albumin excretion, including microalbuminuria (25-249 mg/g) and macroalbuminuria (>or=250 mg/g)). Seventy percent of persons with increased albumin excretion were both normoglycemic and normotensive (systolic/diastolic blood pressure <140/90 mmHg and no use of antihypertensive drugs). Even when diabetic subjects, who have greater risk, were excluded, albumin excretion rose continuously as blood pressure increased among Blacks; increases started at systolic/diastolic blood pressures of 130/85 mmHg among Whites. Furthermore, blood pressure measured up to 15 years earlier predicted incident higher albumin excretion at year 15. These findings persisted after adjustment for age, body mass index, smoking, and blood lipid and plasma insulin levels. A risk of higher urinary albumin excretion exists at blood pressure levels below those commonly regarded as hypertension, with a greater risk among Blacks than among Whites.