In order to verify whether finger photoplethysmographic beat-to-beat recording of blood pressure (BP) can be used to study short-term BP variability, we analyzed by spectral analysis 512-beats SBP stationary sequencies recorded on 36 patients during supine bed rest, active standing, and controlled respiration (CR) at 20 breaths/min. A space state model of the mean was adopted to account for very low frequencies. Spectral analysis of low-(LF, ≈ 0.10 Hz) and high-frequency (HF, ≈ 0.25 Hz) peaks was performed by an autoregressive (AR) method. LF peak spectral power increased during orthostatism (51.35± 10.10 vs 28.70± 25.10, percent power in normalized units), and HF peak increased during CR (77.10± 28.99 vs 58.80± 27.70). A mixed model analysis of variance, performed on sequencies recorded at rest and during active standing, showed that within- and between- subject variabilities were significantly lower than the variability due to the experimental protocol. These results show that noninvasive BP recording from the finger can be reliably used to study short-term BP variability by spectral analysis. This approach will presumably prove most useful in the comparison of groups of patients and in the study of BP response to selected stimuli.