Objective: To evaluate the reliability of a noninvasive hemodynamic monitor in hemodialysis patients., Methods: We enrolled 15 male patients (mean age 63+/-12 years) on stable chronic hemodialysis. Blood pressure and hemodynamic readings were obtained with the Dynapulse 500 Guardian device (Pulsemetric Inc., San Diego, California, USA), which measures systemic hemodynamics on the basis of oscillometric waveforms obtained through a cuff placed over the brachial artery. Measurements were taken sequentially, in duplicate, before, during and after hemodialysis, in the supine, seated and standing positions on four separate midweek dialysis sessions over a 2-week period., Results: The repeatability of the method was tested using 200 pairs of valid measurements. The average values (+/-SD) were 137+/-22 mmHg for systolic blood pressure, 80+/-13 mmHg for diastolic blood pressure, 76+/-15 bpm for heart rate, 1320+/-268 mmHg/s for dP/dtmax, 2.8+/-0.5 l/min/m for cardiac index, and 1455+/-359 dyn/s/cm for systemic vascular resistance. The mean differences (+/-SD of the difference) between readings were 0.1+/-10.4 mmHg for systolic blood pressure, 0.3+/-6.0 mmHg for diastolic blood pressure, -0.2+/-8.0 bpm for heart rate, 0.2+/-234 mmHg/s for dP/dtmax, 0.03+/-0.26 l/min/m for cardiac index and -10+/-177 for systemic vascular resistance, yielding limits of agreement (95%) of -20 to 20 mmHg for systolic blood pressure, -11 to 12 mmHg for diastolic blood pressure, -16 to 17 bpm for heart rate, -458 to 458 mmHg/s for dP/dtmax, -0.5 to 0.5 l/min/m for cardiac index and -338 to 357 dyn/s/cm for systemic vascular resistance. Other hemodynamic parameters fared similarly, and coefficients of variation were all between 7 and 18%., Conclusion: We conclude that the Dynapulse 500 Guardian has adequate reliability indices in hemodialysis patients.