Objective. To evaluate the occurrence and clinical significance of lipid peroxidation (oxidative stress) in rheumatic diseases characterized by vascular involvement. Patients and methods. Plasma 8-epi-PGF 2a (oxidative stress marker) was measured by gas chromatography-mass spectrometry in 36 patients with systemic lupus erythematosus (SLE), 13 with systemic sclerosis (SSc), 13 with systemic vasculitis [ Wegener's granulomatosis ( WG), n = 4; Churg-Strauss syndrome (CSS ), n = 3; Behçet

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... n = 6 ], 12 with rheumatoid arthritis (RA) and in 23 healthy controls (n = 23). Results. 8-epi-PGF 2a levels were higher in patients with SLE (P = 0.007), SSc (P < 0.001) and vasculitis (P = 0.001) than in controls. In SLE, a positive Coombs' test and arterial hypertension independently predicted 8-epi-PGF 2a concentrations (P = 0.004 and P = 0.001, respectively). SLE patients not taking prednisolone showed higher 8-epi-PGF 2a concentrations than SLE patients on prednisolone (P = 0.02). In the latter group, a dose-response relationship was noted between 8-epi-PGF 2a and steroid dosage (r = 0.6, P = 0.0003). In WG and CSS, 8-epi-PGF 2a concentrations correlated with disease activity (r = 0.8, P = 0.01) and were higher than in patients with Behçet disease (P = 0.003). Conclusions. Oxidative stress may be pathogenetically relevant in some autoimmune rheumatic diseases with vascular involvement. Amelioration of some clinical manifestations of these diseases may be envisaged by targeting lipid peroxidation with dietary or pharmacological antioxidants.