BACKGROUND: Only few data are available on reproducibility over time in healthy young men and women and the corresponding gender-related changes of heart rate variability (HRV) measurements. METHODS: We studied temporal and spectral HRV indices obtained from 24-hour Holter recordings in 32 healthy volunteers (14 men and 18 women, mean age 29 +/- 3 years) during 2 days of their usual all-day activity. RESULTS: Time-domain measures and the spectral low-frequency (LF) and high-frequency (HF) components as well as the LF/HF ratio were comparable on both test days. Significantly higher values on test day 2 were observed only for the spectral very-low-frequency (VLF) component and for the resulting total power. Compared to men, women had higher day- and nighttime vagus-associated HRV indices, including root mean square of successive differences (RMSSD), pNN50 (NN50 count divided by the total number of all NN intervals), and HF power, and lower day- and nighttime VLF and LF power with lower LF/HF ratio and total power. CONCLUSIONS: Temporal indices and the LF and HF spectral HRV measures are reproducible over usual all-day activity in young healthy subjects. Young women have higher day-and nighttime vagal tone than men with similar age range.