['Granulocyte-colony stimulating factor (G-CSF) is used for the mobilization of bone marrow and endothelial progenitor cells, though G-CSF-induced inflammation may cause endothelial dysfunction. We examined the effects of G-CSF on endothelium, C-reactive protein (CRP), tumour necrosis factor-alpha (TNF-alpha) and anti-inflammatory cytokines namely interleukin 10 (IL-10).', 'We studied 60 women with breast cancer, who were randomized to either subcutaneous G-CSF (5 microg/kg), o.d. for 5 days after adjuvant chemotherapy (n = 40) or placebo (n = 20).', 'We measured flow-mediated dilatation (FMD%) of the brachial artery by ultrasonography, CRP, TNF-alpha, IL-10 and the ratio TNF-alpha/ IL-10 blood levels before, 2-h and 5-days after the G-CSF or placebo treatment.', 'There was a greater increase of FMD, IL-10 and reduction of TNF-alpha/ IL-10, 2 h and 5 days after the G-CSF treatment compared to placebo. Although, CRP and TNF-alpha were higher, TNF-alpha/IL-10 was lower at the end of G-CSF treatment compared to placebo. Improvement of FMD was related to changes of IL-10 and TNF-alpha/IL-10.'] Is treatment with granulocyte colony stimulating factor associated with improvement in endothelial function?