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The number of hematopoietic stem cells (HSC) and endothelial progenitor cells (EPC) is thought to be a marker for neovascularization and vascular repair. Because physical inactivity and aging are risk factors for cardiovascular diseases, these factors may influence the numbers of HSCs and EPCs. Therefore, we examined baseline and exercise‐induced levels of HSCs and EPCs in sedentary and trained young and older men. To study the role of aging in eight sedentary young (19–28 years) and eight sedentary older men (67–76 years), baseline and acute exercise‐induced numbers of HSCs (CD34⁺‐cells) and EPCs (CD34⁺/VEGFR‐2⁺‐cells) were quantified by fluorescence‐activated cell sorter (FACS) analysis. To examine the effect of chronic training, eight age‐matched trained young men (18–28 years) were compared with sedentary young men, whereas older men performed an 8‐week endurance training …