This study was to assess left ventricular diastolic function in young white-coat hypertensive subjects <50 years of age without hypertrophy. Hypertensive patients (systolic or diastolic blood pressure greater than or equal to 140 or greater than or equal to 90 mm Hg on all three visits) were defined as while coat if their average 24-hour blood pressure was <127/81 mm Hg and at least 18/16 mm Hg lower than their average office values. We chose three groups balanced for sex, age, and body mass index: 50 sustained hypertensives, 25 white-coat hypertensives, and 25 normotensives. Office blood pressure was similar in white-coat and sustained hypertensives. Ambulatory blood pressure was comparable in white-coat hypertensives and normotensives. Compared with normotensives, white-coat hypertensives had more impaired diastolic function: increased ratio of late to early filling velocities, raised ratio of late to early time-velocity integral, prolonged deceleration time, and lengthened isovolumic relaxation time (P<.001, P<.001: P=.002, and P<.001, respectively). No difference was noticed between white-coat and sustained hypertensives. Compared with normotensives, white-coat hypertensives had higher values of plasma and urine norepinephrine (P<.001 and P<.001, respectively), plasma and urine aldosterone (P<.001 and P=.002, respectively), plasma renin activity (P=.04), total cholesterol (P=.001): and LDL cholesterol (P<.001). No difference was observed between white-coat and sustained hypertensives. Within white-coat hypertensives, 24-hour urinary aldosterone closely correlated with the ratio of late to early filling velocities (P=.008), and plasma and 24-hour urinary norepinephrine correlated well with total cholesterol (P=.037 and P=.006, respectively). No correlation was detected within the sustained hypertensives and normotensives. Heightened neurohumoral activity clearly supported the progression of diastolic dysfunction and metabolic abnormality in white-coat hypertensives.