1. The plasma brain natriuretic peptide (BNP) concentration is elevated in patients with essential hypertension and normal systolic function. This may be related to left ventricular hypertrophy or diastolic dysfunction, both of which commonly occur in hypertension. 2. Echocardiography was performed on 32 patients with newly diagnosed untreated mild-to-moderate hypertension (19 men, 13 women; mean +/- SD age 51 +/- 15 years; diastolic blood pressure 99 +/- 12 mmHg; systolic blood pressure 153.2 +/- 18.0 mmHg; plasma creatinine 86 +/- 15 mumol/L; creatinine clearance 92.2 +/- 20.5 mL/min; left ventricular mass index 116 +/- 28 g/m2; left ventricular ejection fraction 66 +/- 9%). A 15 mL peripheral venous blood sample was obtained at the time of echocardiography for radioimmunoassay of BNP. 3. Sixteen patients had abnormal Doppler transmittal flow (E/A ratio < 1) and a higher median plasma BNP concentration compared with those patients with E/A > or = 1 (12.9 vs 5.9 pmol/L, respectively; P = 0.006). The plasma BNP level correlated significantly with E/A ratio (r = -0.50; P = 0.035). Multivariate analysis showed that the E/A ratio is related to plasma BNP, independent of age and blood pressure. 4. Our results suggest that the plasma BNP level is influenced by diastolic dysfunction. Further studies are needed to determine whether assay of plasma BNP helps to identify patients with diastolic dysfunction.