Blood endothelial progenitor cells (EPC) and microparticles (EMP) have been proposed as markers of endothelial dysfunction. The aim of this study was to evaluate both EPCs and EMPs in patients with arterial erectile dysfunction (ED) and metabolic syndrome (MetS). To accomplish this, 100 patients (ages 45-60 years) with ED and MetS (Adult Treatment Panel III [ATP III] 1999 criteria) and 17 healthy men (ages 44-57 years) were selected. EPC (CD45(neg)/CD34(pos)/CD144(pos)) and EMP (CD45(neg)/CD144(pos)/Annexin V(pos)) blood concentrations were evaluated by flow cytometry, before and after administration of tadalafil (20 mg) on demand for 3 months. Before treatment, EPCs and EMPs were significantly higher in patients compared with healthy men. EPCs increased significantly after tadalafil administration, whereas EMPs did not differ significantly. EPCs correlated positively or negatively with body mass index and with some cavernous artery indices, both before and after tadalafil administration. EMPs showed only positive correlations with body mass index and some cavernous artery indices, both before and after tadalafil administration. Patients with arterial ED and MetS have higher EPCs and EMPs compared with healthy men; hence, these cells may be regarded as markers of cavernous artery dysfunction. Tadalafil administration increased EPCs but not EMPs, suggesting that this compound may play a role in the endothelial repair response.