The study aimed at determining the presence of an oxidative stress in patients with macrophagic myofasciitis (MMF), a new inflammatory myopathy with suspected toxic etiology related to aluminium hydroxide-containing vaccines. A total of 30 MMF patients (nine males, 21 females; aged 42+/-14 years), whose diagnosis was confirmed by deltoid biopsy, have been included and compared to 38 sex- and age-matched healthy control subjects (10 males, 28 females; aged 43+/-8 years). The blood oxidative stress status has been evaluated by assaying six parameters: plasma lipid peroxidation products (thiobarbituric acid-reactive substances: TBARS) and antioxidant defense systems: plasma vitamin E and glutathione peroxidase (GSH-Px) activity, erythrocyte GSH-Px and Cu,Zn-superoxide dismutase (SOD) activities. Plasma selenium was also determined as a trace element essential to the activity of GSH-Px. Statistical significance was evaluated by the Mann-Whitney test. Plasma GSH-Px activity, selenium and vitamin E concentration were significantly lower in MMF group than in controls (P=0.004, P=0.003 and P=0.009, respectively), with a positive correlation in MMF patients between plasma GSH-Px activity and selenium concentration (rho=0.0001). The other parameters of oxidative stress did not significantly differ between both groups. A macrophage activation could occur in MMF, consequently to chronic stimulation by aluminium-containing vaccines, and could participate to the lower values of selenium and vitamin E observed in comparison with controls. Nevertheless, since no deficiency in these elements has been observed, no supplementation is to be considered.