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.