BACKGROUND AND OBJECTIVES: This study was performed to, 1) evaluate the diagnostic value of the Brain Natriuretic Peptide (BNP), which is known to be present in the heart ventricle, for patients with dyspnea for the assessing its causes;diastolic or systolic heart failure or pulmonary disease, and 2) find if the BNP is correlated with the distance walked in 6 minutes, which is known to be a prognostic indicator for heart failure. SUBJECTS AND METHODS: Fifty-seven patients who admitted to the Kangbuk Samsung Medical Center, with the chief complaint of dyspnea, were enrolled in the study. The subjects were classified into three groups according to the causes of their dyspnea, which were systolic heart failure, diastolic heart failure and chronic obstructive pulmonary disease. The plasma BNP levels were measured by a radioimmunoassay, both at admission and discharge. The BNP levels at admission were compared among the three groups. The presence of a correlation between the distance walked in 6 minutes and the BNP at discharge were also evaluated. RESULTS: The patients group with systolic heart failure had the highest mean BNP concentration of 934.6+/-386.7 pg/mL. The other two groups had significantly lower levels of BNP. The patients group with chronic obstructive pulmonary disease had significantly lower level than the group with diastolic heart failure (33.2+/-25.6 vs. 181.8+/-222.2 pg/mL). The BNP concentrations at discharge, and the distance walked in 6 minutes, between the three groups showed no statistical significance (p=0.69). CONCLUSION: This study showed that the mean plasma BNP level was highest in the group with systolic heart failure, followed by diastolic heart failure and lastly chronic obstructive pulmonary disease. These findings suggest that diagnostic value of the plasma BNP concentration in the assessment of the causes of dyspnea. Although this study has failed to show a correlation between the plasma BNP concentration at discharge and the distance walked in 6 minutes, prospective cohort studies, with larger sample sizes, need to be performed to establish the relationship, if any.