Recombinant human G-CSF (rHuG-CSF) is used for hematopoietic progenitor cells (HPC) mobilization and collection. Activation of polymorphonuclear leukocytes (PMN) is present during rHuG-CSF treatment and is associated with endothelial cell dysfunction and hypercoagulation. We evaluated whether PMN activation by rHuG-CSF may alter the blood oxidative status and subsequently affect the vascular cell function. Fourteen healthy individuals received rHuG-CSF for HPC harvesting. Blood was drawn before starting rHuG-CSF (T0), on the last day of rHuG-CSF (T1) and 1 week after stopping rHuG-CSF (T2). Levels of CD11b, myeloperoxidase (MPO), hydroperoxides, nitric oxide (NO), and soluble endothelium (sES), leukocyte (sLS), and platelet (sPS) selectins were measured. During rHuG-CSF, CD11b, MPO and hydroperoxides significantly increased, while NO levels significantly decreased, compared with T0. At T2 all these markers returned to baseline values. Significant increments of all selectins were observed during rHuG-CSF. At T2 sES and sEP significantly decreased back to pre-treatment values, whereas sLS remained significantly high. These data show that rHuG-CSF induces a transient inflammatory status characterized by circulating activated PMN, which release reactive oxygen species and intracellular proteases, promoting the onset of an abnormal oxidative status. This process may modify the hemostatic balance towards a pro-thrombotic state.