OBJECTIVE To determine the effects of exercise training on calf tissue oxygenation in men with peripheral arterial disease and intermittent calf claudication. METHODS This pilot study was prospective and longitudinal and used a one-group, pretest-posttest design. METHODS Tertiary care medical center for veterans. METHODS Fifteen male veterans (mean age 69 years) with Fontaine stage IIa peripheral arterial disease and classic intermittent claudication. METHODS Before and after intervention, participants performed graded treadmill exercise tests while medial calf tissue oxygenation (StO(2), % oxyhemoglobin saturation) was monitored continuously with near-infrared spectroscopy. METHODS The intervention consisted of a 3-month exercise training program involving 3 sessions per week at the clinic (treadmill walking, calf ergometry) and 2 sessions per week at home (free walking, standing heel raises). RESULTS After completion of the intervention, participants significantly increased their maximal treadmill exercise time from 7.19 to 11.27 minutes. Mean exercise StO(2) decreased from 29% to 19% saturation, StO(2) x time area increased from 421% * min to 730% * min StO(2) nadir, and StO(2) recovery time did not change significantly. CONCLUSIONS After the exercise intervention, the improved treadmill walking performance was accompanied by greater calf tissue deoxygenation during exercise. Given the continued presence of ischemia, this finding may represent increased capillarization and diffusion-based enhancement of arteriovenous O(2) extraction.