The mammalian heart synthesises and secretes B-type natriuretic peptide (BNP), which has potent diuretic, natriuretic and vascular smooth muscle-relaxing effects as well as complex interactions with the hormonal and nervous systems. Recent studies described that BNP was acute phase reactant. In this study, we aimed to evaluate BNP levels in patients with pneumonia. Twenty-one patients with pneumonia and 21 healthy control subjects were enrolled in this study. Their serum levels of BNP were measured in addition to the standard evaluations. Leucocyte count [19.3 (13.2-25.7) 10(6)/Ml VS. 9.55 (3.7-13.9) 106/Ml, p < 0.0011, erythrocyte sedimentation rate [73 (57-81) mm/h vs. 35 (4-55) mm/h, p < 0.001], C-reactive protein (CRP) [127.72 (27-290) mg/l vs. 13.19 (3-41) mg/l, p < 0.0011 and BNP [53.1 (17-91) pg/ml vs. 16.24 (1-38) pg/ml, p < 0.0011 levels significantly decreased after treatment period. Initial BNP levels were significantly higher than control groups (53.10 +/- 15.07 pg/ml vs. 18.62 +/- 14.05 pg/ml, p < 0.001) and decreased after treatment to the levels comparable with control subjects. BNP levels correlated with CRP levels at admission (r = 0.716, p < 0.001). We have shown that BNP levels show a transient increase in patients with pneumonia and correlate well with CRP.