Short period oscillatory components embedded in heart rate variability (HRV) were studied during hemodialysis induced hypovolemia in 15 hypotension-resistant (stable) and 15 hypotension-prone (unstable) patients. Hemodialysis was undertaken so that a similar blood volume reduction was induced in all patients (p > 0.05) without causing acute hypotension events. Autoregressive HRV power spectrums were calculated using an eigenanalysis-based approach. The frequencies of the main HRV rhythmic components were estimated through the Pisarenko harmonic decomposition. Percent changes during the hemodialysis in both heart rate and arterial pressure were similar in the stable and unstable groups (p > 0.05). The HRV spectral density showed markedly different power distributions. In the stable patients, power was mainly in the low frequency band (74+/-7 nU in the low frequency [LF] band vs. 21+/-6 nU in the high frequency [HF] band) whereas in stable patients, it was mainly in the high frequency band (39+/-10 nU in the LF band vs. 47+/-7 nU in the HF band). The frequency of the main oscillation was 0.1+/-0.02 Hz in stable patients and 0.18+/-0.04 Hz in unstable ones (p < 0.01). These HRV spectral parameters have a clear diagnostic value in discriminating between stable and unstable patients when their hemodynamic behaviors are similar.