Elevated plasma brain natriuretic peptide (BNP) levels have been described in patients with acute myocardial infarction and left ventricular dysfunction. The aim of the present study was to evaluate circulating BNP levels in patients with coronary artery disease without ST-segment elevation acute myocardial infarction and preserved systolic function and to evaluate the BNP levels in relation to the number of involved coronary vessels. We studied 88 patients with coronary artery disease: group 1 had stable angina, group 2 had unstable angina (UA), group 3 had non-Q-wave myocardial infarction (NSTEMI), and group 0 consisted of 15 healthy subjects. All recruited subjects underwent angiographic examination and echocardiographic evaluation. No patients had heart failure, previous myocardial infarction, or electrocardiographic ST elevation. A significant increase in BNP levels was observed in the UA and NSTEMI groups compared with the stable angina group (stable angina 31.3 pg/ml, UA 147.3 pg/ml, NSTEMI, 165.8 pg/ml, p <0.01), and no differences were found between the UA and NSTEMI groups. Analysis of BNP in relation to the number of involved vessels showed significantly higher BNP levels in patients with 3- than in those with 1- or 2-vessel disease (1 to 45.2, 2 to 127.3, and 3 to 220.8 pg/ml, respectively, p <0.05 and p <0.0001, 3 vs 1- and 2-vessel disease, p = 0.01, respectively). Patients with left anterior descending stenosis had higher BNP levels than those with stenosis in other areas (150.8 vs 52.2 pg/ml, p <0.01). In conclusion, circulating BNP levels appeared elevated in patients with acute coronary syndromes with diffuse coronary involvement, even in the absence of systolic dysfunction or heart failure. BNP was also associated with multivessel disease and left anterior descending involvement.