A total of 124 prepubertal males and females were followed longitudinally for five years. Yearly examinations defined the stages of sexual maturation. On four occasions each year, subjects were studied for resting and ambulatory blood pressure, echocardiography, anthropometry and activity assessment. Once yearly, each subject had blood drawn for hormone analyses and whole blood viscosity estimate. From these data, growth velocities of the heart and rate of change of blood pressure were determined. These parameters were analyzed to determine if rapid growth of the heart preceded or followed the rise in blood pressure observed during puberty and body size and composition, sexual maturation and hormone changes, and sympathetic activity.