OBJECTIVE To evaluate the influence of different clinical and echocardiographic parameters on left ventricular diastolic filling in 66 mild to moderate hypertensives and 49 normotensives. METHODS All subjects underwent an echocardiographic study with a pulsed Doppler evaluation of left ventricular filling. The hypertensive subjects also underwent non-invasive 24-h blood pressure monitoring. RESULTS The ratio of early to atrial peak diastolic filling velocity and the ratio of the corresponding areas under the curve (AUC) were significantly lower in the hypertensives compared with the normotensives (P less than 0.001). In the hypertensives, office blood pressure, average 24-h mean blood pressure, the left atrial dimension and the left ventricular mass index were each related both to age and to diastolic filling. The variable most closely related to diastolic filling independently of age and the R-R interval was 24-h blood pressure (ratio of early: atrial peak filling velocity versus 24-h blood pressure: r = -0.307, P less than 0.05; ratio of early: atrial AUC versus 24-h blood pressure: r = -0.261, P less than 0.05). When the normotensives and hypertensives were each grouped according to age less than or equal to or greater than 40 years, the normotensive-hypertensive mean difference was greater in the subjects aged greater than 40 years for both the early:atrial maximal velocity ratio and the early:atrial AUC ratio. CONCLUSIONS Age is the strongest clinical correlate for left ventricular diastolic function indices, in both hypertensives and normotensives. In the present study, average 24-h blood pressure and, to a lesser extent, the heart rate were also associated with an impaired diastolic performance.