This study was undertaken to prospectively evaluate and compare the acute effect of high-dose (HD), cyclophosphamide (CY) and HD etoposide (ET) on cardiac function assessed by plasma N-terminal pro-B-type natriuretic peptide (NT-proBNP) in patients undergoing stem-cell mobilization. NT-proBNP was measured at baseline and 6 h after completion of mobilization chemotherapy (MC) in 58 patients. Of 58 patients, 33 received HD CY, and 25 received HD ET. The mean baseline NT-proBNP values were similar between the CY and ET group (119.5 vs 149, respectively, p> 0.05). NT-proBNP levels were increased in almost all patients, except 2 from CY group. A significant difference between NT-proBNP concentrations at baseline and 6 h after completion of MC was observed in both groups (p < 0.001). The value of changes in NT-proBNP was more significant in the ET group. The changes in NT-proBNP according to the MC regimens were analyzed and a cut-off value of 422 pg/ml was determined. Based on this cut-off value, only the type of MC was significantly correlated with the chances in NT-proBNP concentrations. Receiving HD ET as a MC was found to be 5.25 times more cardiotoxic compared to the HD CY. Congestive heart failure was seen in 3 (5.2%) patients. Our results suggest that stem cell mobilization with HD CY and HD ET cause acute cardiac toxicity mediated by neurohumoral activation, which was detected by the increases in cardiac biomarker NT-proBNP, and as a matter of fact cardiotoxicity of HD ET seems to be more potent than those exhibited by HD CY. (C) 2013 Elsevier Ltd. All rights reserved.