Background - Previous studies utilizing detrended fluctuation analysis (DFA) technique to analyze heart rate variability during sleep revealed higher fractal exponent during rapid eye movement (REM) sleep than non-rapid eye movement (NONREM) sleep. The aim of this study was to determine if the same REM-related long-term correlations also exist in the variations of peripheral arterial tone in three independent groups of patients with congestive heart failure (CHF), heavy snorers and normal controls. Methods and results - Sleep was monitored and peripheral arterial tone was recorded in 12 CHF patients (age range: 41-80 yrs), 8 adults with heavy snoring (age range: 31-66 yrs), and 12 young adults healthy volunteers (age range: 16-45 yrs). For each subject, at least two 15-minute time series were constructed from the inter-pulse intervals and from the pulse wave amplitudes during REM and sleep stage 3-4 (NONREM) sleep. Fractal scaling exponents for all three groups obtained by DFA of the pulse wave interval and pulse wave amplitude time series, were significantly higher for REM than sleep stage 3-4. In each of the groups and in both sleep stages, the fractal scaling exponents based on pulse wave amplitude were significantly higher than those based on pulse rate variability. Across groups, age was significantly correlated with the fractal exponent based on the pulse wave amplitude during both REM and sleep stage 3-4. A repeat of the analysis for short-, intermediate-, and long-term intervals, revealed that the fractal-like exponents were evident only in the short- and inetrmediate-term intervals. Conclusions - Variations in peripheral arterial tone during REM sleep show fractal correlation properties which are similar to those shown in heart rate variability previously. Since peripheral arterial tone is a surrogate of sympathetic activation, it indicates that variations in the sympathetic activation during REM sleep have a fractal-like behavior.