To investigate the levels of B-type natriuretic peptide (BNP) in patients with atrial fibrillation (AF) but without structural heart disease, we measured plasma BNP concentration in 61 consecutive AF patients and in 61 age- and sex-matched healthy subjects. Plasma BNP concentration in the AF group was significantly higher than in the control group (121+/-32 vs 41+/-12 pg/ml, P<0.001). Logistic regression analysis showed that age (r=0.66, P<0.001), left atrial diameter (r=0.59, P<0.01), and a history of AF (r=0.72, P<0.001) were independent predictors of elevated BNP. We concluded that BNP was elevated in patients with paroxysmal lone AF. The clinical significance of BNP elevation in these patients requires further investigation.