We have used near-infrared spectroscopy to measure the hemoglobin saturation at rest and during exercise on patients affected by peripheral vascular disease (PVD). The instrument used in our study is a frequency-domain tissue oximeter which employs intensity modulated (110 MHz) laser diodes. We examined 9 subjects, 3 of which were controls and 6 were patients affected by stage II PVD. The optical probe was located on the calf muscle of the subjects. The measurement protocol consisted of: (1) baseline (∼5 min); (2) stationary bicycle exercise (∼5 min); (3) recovery (∼15 min). The change in hemoglobin saturation during exercise (ΔY) and the recovery time after exercise (trec) were significantly greater in the PVD patients (ΔY = -21±3%, trec= 5.9±3.8 min) than in the control subjects (ΔY = 2±3%, trec = 0.6±0.1 min).