Trauma, inflammatory disorders and other perturbations induce the so-called acute phase response in organisms. The phenomenon encompasses many physiological alterations including typical changes in plasma proteins. Often an accumulation and activation of superoxide radical-producing leucocytes occurs at the site of perturbation. The major enzymic protector against superoxide radicals in plasma and other extracellular fluids is extracellular-superoxide dismutase. The acute phase response of extracellular-superoxide dismutase was investigated in two groups, one comprising 13 patients in the postoperative period after surgical trauma and the other 15 patients with various inflammatory disorders. No significant positive or negative acute phase response of plasma extracellular-superoxide dismutase was revealed.