UNLABELLED: Serum brain natriuretic peptide (BNP) has been reported to indicate ventricular dysfunction, however, in children it has not been studied yet in our country. PURPOSE: 157 BNP tests were performed in 107 children, on the one hand, to evaluate its clinical value, to assess LV or systemic RV function in patients with transposition of great arteries after Senning operation, on the other hand, to prove the relation between BNP, MRI and echocardiographic ventricular function parameters. PATIENTS' AGE: 4 months-20 years, mean 12.5 yrs. Group I: Senning patients, Groups II and III: patients with dilated or hypertrophic cardiomyopathy, Group IV: patients with aortic insufficiency. METHODS: BNP was determined using the electrochemiluminesce method (Elycsys-10 Roche). During the functional MRI Mass- Medis software RV LV EF, end-diastolic, end-systolic volumes were calculated. Echo M-mode, TEI index were calculated. RESULTS: BNPs were significantly as higher compared to normal in each group of patients. Group I: 318 +/- 285 pg/ml, p < 0.01, Group II: 7262 +/- 10970 pg/ml, p < 0.01, Group III: 1558 +/- 2765 pg/ml, p < 0.01, Group IV: 1076 +/- 2791 pg/ml, p < 0.00l, vs 58 +/- 31 pg/ml. BNP were negatively correlated with MRI RV EF (r: -0.51, p < 0.05) and showed good correlation with TEI index (0.43 +/- 0.18, p < 0.05). After 3 weeks of medical or surgical treatment BNP decreased significantly. 4 patients died during the follow-up period, these had the highest BNP levels in each patients group. CONCLUSIONS: BNP is a useful, prognostically valuable method in children to monitor ventricular function. BNP levels reflect the severity of the impairment of systemic RV function in Senning patients in whom a complex RV geometry is present causing the assessment of RV function more difficult, so we recommend BNP measurements as a longitudinal test in this patient group.