We examined the relationship between plasma B-type natriuretic peptide (BNP) level and diurnal variability pattern of blood pressure (BP). Twenty-four-hour ambulatory BP monitoring was performed in 98 patients with asymptomatic essential hypertension, and the patients were classified into four groups according to their circadian BP variation profiles: dippers (n=29), nondippers (n=36), extreme dippers (n=19), and risers (n=14). Plasma BNP was measured by enzyme immunoassay. Based on the distribution pattern of BNP values, the values were analyzed after logarithmic transformation. Significant differences in plasma BNP levels among the types of circadian BP variations were demonstrated by analysis of variance (p<0.0005). Nondippers and risers showed significantly higher plasma BNP levels (mean [range: -1 SD and +1 SD]: 16.1 [6.3, 41.6] pg/mL and 29.2 [15.9, 53.4] pg/mL, respectively) than dippers (8.4 [3.7, 19.1] pg/mL). The area under the receiver operating characteristics curve for distinguishing patients with abnormal circadian BP variation from those with normal variation was 0.72, indicating that plasma BNP levels were useful for distinguishing between these patients. Specificity of 69% and sensitivity of 72% were obtained with a cut-off value of 10.5 pg/mL (log plasma BNP, 1.02) for distinguishing the abnormal diurnal BP profile group from the normal group. In conclusion, hypertensive patients with abnormal diurnal BP variation patterns (nondippers, extreme dippers, and risers) showed higher plasma BNP levels than those with normal circadian BP variation (dippers). Plasma BNP level is clinically useful for the identification of hypertensive patients who have abnormal circadian BP variability, which increases the risk of cardiovascular events.