In a series of 35 newly diagnosed, previously untreated patients (mean age 46 years) with mild to moderate essential hypertension, office blood pressure measurements, 24-hour ambulatory blood pressure monitoring, and determination of left ventricular mass index by echocardiography according to the formula of Devereux were performed. We aimed at correlating left ventricular mass index with systolic and diastolic office blood pressure, mean 24-hour systolic and mean 24-hour diastolic blood pressure, systolic and diastolic load. Left ventricular mass index did not correlate with office systolic and office diastolic blood pressure. On the contrary, all correlations with ambulatory blood pressure parameters and left ventricular mass index turned out to be significant (mean 24-hour systolic blood pressure: r = 0.344, P = 0.026; systolic load: r = 0.408, P = 0.020; mean 24-hour diastolic blood pressure: r = 0.490, P = 0.004; diastolic load: r = 0.504, P = 0.003). These results clearly demonstrate that ambulatory blood pressure determinants but not the office blood pressure parameters are well correlated with left ventricular mass index in mild to moderate essential hypertension. Blood pressure load is as important as mean 24-hour blood pressure in this regard.