<b><i>Background/Aims:</i></b> This study investigates the use of blood volume monitoring (BVM) markers for the assessment of fluid status. <b><i>Methods:</i></b> Predialysis fluid overload (FO) and BVM data were collected in 55 chronic hemodialysis patients in 317 treatments. Predialysis FO was measured using bioimpedance spectroscopy. The slope of the intravascular volume decrease over time normalized by ultrafiltration rate (Slope4h) was used as the primary BVM marker and compared against FO. <b><i>Results:</i></b> Average relative blood volume curves were well separated in different FO groups between 0 and 5 liters. Receiver-operating characteristics analysis revealed that the sensitivity of BVM was moderate in median FO ranges between 1 and 3 liters (AUC 0.60-0.65), slightly higher for volume depletion of FO <1 liter (AUC 0.7) and highest for excess fluid of FO >3 liters (AUC 0.85). <b><i>Conclusion</i></b>: Devices that monitor blood volume are well suited to detect high FO, but are not as sensitive at moderate or low levels of fluid status.