In the cross-sectional CARDIA investigation, studies were conducted on the relationships among lithium countertransport, blood pressure, and factors related to blood pressure such as age, sex, race, weight, body mass index, pulse, dietary factors, alcohol intake, serum glucose, triglycerides, cholesterol, high density lipoprotein cholesterol, uric acid, and ionized and total calcium. Prospective data were also collected from TOMHS to examine whether lithium countertransport was modified in mild hypertension by diet or by a combination of diet and antihypertensive drugs. Lithium countertransport was assayed in erythrocytes at the second examination in CARDIA and at baseline, 12 months, and 24 months in TOMHS.