In order to assess an impact of acute changes in blood volume on levels of B-type natriuretic peptides (BNP and NT-proBNP) 30 patients with a heart disease and chronic renal insufficiency on chronic dialysis program were assessed. An acute fluid restriction of 3750 ml on an average lead to decreased filling of the left heart ventricle (echocardiography revealed a reduced size of the left atrium, change in E/A parameters and deceleration time, and decreased end-diastolic volume of the left ventricle). Prior to dialysis normal levels of BNP (2.58 +/- 1.21 pg/ml) and elevated levels of NT-proBNP (193.2 +/- 117.7 pg/ml) had been indicated. Following dialysis a statistically significant decrease of BNP concentration in venous blood was proved, however it was "masked" by hemoconcentration. NT-proBNP level in venous blood remained unchanged. Correlation between BNP and NT-proBNP was not proved before dialysis nor after it. Correlation between BNP levels and echocardiographic parameters was not confirmed and a weak negative correlation with ejection fraction was proved in NT-proBNP. A BNP assessment could play an important role in the evaluation of acute changes in heart compensation. On the other way, NT-proBNP concentration is stable and is a long term marker of synchronisation of fluid circulation and function of the left ventricle. An importance of its assessment is probably rather prognostic.