Background: B-type natriuretic peptide (BNP) was reported to be somewhat increased after exercise in healthy adults as well as the patients with hypertension. However, the relationship between changes of BNP and left ventricular filling pressure, or determinants of plasma BNP concentration after exercise has not fully evaluated. Methods: Fifty-nine patients who complained exertional dyspnea (Group A, age: 56 짹 11 yr) and 20 young healthy adults (Group B, age: 25 짹 2 yr) underwent a symptom-limited ergometer exercise test, started at 25 W and advanced by 15 W incremental loading every 2 minutes. Baseline echocardiographic examinations were done including mitral inflow Doppler and mitral annulus velocity for measurement of E/E���ratio, and were repeated at the peak exercise. Blood samplings were done before and at the peak exercise for BNP level. Results: Group A revealed significantly higher baseline BNP level (p<0.005) and E/E' ratio (p<0.001), and shorter exercise time (10 짹 4 vs. 17 짹 3 mins, p<0.001) than Group B. In both groups, BNP level (12 짹 15 to 18 짹 25 pg/ml, p<0.001 in Group A, and 5 짹 5 to 10 짹 8 pg/ml, p<0.001 in Group B) and E/E���ratio (13 짹 4 to 15 짹 4, p<0.01 in Group A, and 7 짹 1 to 10 짹 2, p<0.001 in Group B) were significantly increased after exercise. The increment of BNP level or E/E' ratio was not significantly different between the two. Baseline BNP level was significantly correlated with left atrial diameter (r=0.314, p<0.01), baseline E/E���(r=0.223, p<0.05), and age (r=0.272, p<0.05). Peak BNP level was well correlated with baseline BNP level (r=0.950, p<0.001), peak E/E���ratio (r=0.260, p<0.05), and baseline left atrial diameter (r=0.248, p<0.05). However, the increment of BNP was not significantly correlated with the increment of E/E���ratio. Baseline BNP level was the only independent determinant of peak BNP level by multivariate analysis (p<0.001). Conclusion: Plasma BNP concentration is increased after exercise in patients with exertional dyspnea as well as healthy young adults. However, BNP level after exercise seems to be mainly determined by BNP level at rest, not by increment of left ventricular filling pressure after exercise.