Oxidative stress is suggested to be involved in the pathogenesis of systemic sclerosis (SSc). The aim of the present study was to clarify such a hypothesis by determination of four different plasmatic parameters of oxidative stress, and to define its role in the microvascular damage, assessed by nailfold capillaroscopy (NC). Plasma samples of 18 patients with SSc were analyzed. The biomarkers measured were: total antioxidant capacity, hydroperoxides (ROOHs), and sulfhydryl (SH) and carbonyl (CO) groups. Each patient had a detailed clinical assessment and underwent an NC. The results showed significantly increased ROOHs in SSc patients compared to control group (5.02 +/- 0.24 vs 3.28 +/- 0.19 micromol/l; p < 0.05). Plasmatic levels of SH groups were significantly lower in SSc (0.466 +/- 0.08 mmol/l) compared to control group (0.542 +/- 0.04 mmol/l; p < 0.002). Plasma levels of ROOHs correlated with the capillaroscopy semiquantitative rating scale score (p < 0.05) and with the rating system for avascular areas (p < 0.03). The levels of CO groups inversely correlated with modified Rodnan's skin score (p < 0.039) and were lower in patients with pulmonary fibrosis (p < 0.045), while the levels of SH groups were lower in those presenting gastrointestinal involvement (p < 0.029). The obtained data indicate augmented free radical-mediated injury in SSc and also show correlations among oxidative abnormalities, some clinical findings, and signs of a more severe microvascular involvement. These results give more evidence to the connection between oxidative impairment and SSc.