Acute carbon monoxide (CO) poisoning may cause cardiotoxicity. The natriuretic peptides, including atrial natriuretic peptide, brain natriuretic peptide (BNP), N-BNP, and NT-proBNP (N-terminal pro brain natriuretic peptide), are endogenous cardiac hormones that may be secreted upon myocardial stress. The aim of this study was to assess the plasma NT-proBNP level in acute CO poisoning and to compare it with healthy control. After approval by the ethical committee, 15 healthy controls and 15 patients admitted to the Gaziantep University Hospital (Gaziantep, Turkey) between January 2005 and July 2005 with the diagnosis of carbon monoxide poisoning were studied. Echocardiography was performed to all patients. Serum NT-proBNP, creatine kinase (CK), creatine kinase-MB (CK-MB), and troponin-T were also analyzed, along with the carboxyhemoglobin (COHb) level. The correlation between serum NT-proBNP and COHb level was investigated. Electrocardiography (ECG) was performed to all patients and healthy controls, and the results were compared. Differences in troponin, CK, and CK-MB levels were not statistically significant between groups (p > 0.05). The level of NT-proBNP and COHb were found to be increased in the study group. There was a positive correlation between the COHb and the NT-proBNP (r = 0.829, p < 0.01), and between the COHb and the CK (r = 0.394, p < 0.01). There was no difference between groups in other parameters, all of which were within normal range. Thus, in this study we showed that the plasma NT-proBNP level may contribute to the early diagnosis of cardiotoxicity in patients with carbon monoxide poisoning.