In 63 patients affected by Systemic Sclerosis (SSc) (limited subset: 40; diffuse subset: 23; early: 30; advanced: 33) the peroxidation product diene-conjugates (DC) and antibodies against oxidised low density lipoproteins (Ab oxLDL) were tested in serum by a spectrophotometer (absorbance 234 mn) and by a standard ELISA respectively. The data were compared with those obtained by 21 healthy subjects. DC was significantly higher in patients (73.3 +/- 37.2 microM/l; p < 0.0001) than in controls (48.4 +/- 16.7) as well as in the limited (80 +/- 48.8; p < 0.05) than in the diffuse subset (64.5 +/- 36.4); and in early (84.1 +/- 31.4; p < 0.05) than in advanced stage of the disease (67.9 +/- 42.5). The levels of Ab oxLDL were significantly higher in SSc patients (309.5 +/- 367.2 mU/ml; p < 0.0001) in all its subsets (limited: 351.9 +/- 351.1, p < 0.0001; diffuse: 207.7 +/- 316.1, p < 0.05; early: 428.9 +/- 417.1, p < 0.001; advanced: 302.7 +/- 89.9, p < 0.0001) than in controls (89.3 +/- 29.1). These antibodies levels were higher in limited subset than in diffuse (p < 0.05) and in early SSc than in advanced SSc (p < 0.05). The highest values of parameters of oxidative stress are found in the early stages, when the episodes of reperfusion after ischemic episodes (Raynaud's phenomenon) are very frequent. Moreover, the damage is higher in the early stages of SSc, with intact microvessels, than in late stages, when microvessels are very reduced in number, destroyed by the worsening of the disease. These data show that the respiratory burst deduced by the lipoperoxidation is higher in SSc than in controls, and may be an important pathogenetic factors involved in tissue changes in SSc.