Oxygen free radicals as well as immunological reactions have been suggested to play important roles in atherogenesis and other pathological processes of the blood vessel wall. We have previously shown that the vascular wall contains exceptionally large amounts of extracellular superoxide dismutase (EC-SOD) and that the enzyme is produced and secreted to the extracellular space by the smooth muscle cells. In this work, we studied the influence of inflammatory cytokines on vascular smooth muscle cell expression of EC-SOD, the mitochondrial manganese superoxide dismutase (Mn-SOD) and the cytosolic copper zinc superoxide dismutase (CuZn-SOD). The expression of EC-SOD was up-regulated by interferon-gamma (IFN-gamma) and interleukin 4 (IL-4). and was down-regulated by tumor necrosis factor-alpha (TNF-alpha). The ratio between the maximal stimulation and depression observed was around 20-fold. The responses were slow and developed over periods of several days. The Mn-SOD activity was strongly up-regulated by TNF-alpha and IL-1alpha and moderately by IFN-gamma. The CuZn-SOD activity of the smooth muscle cells was not significantly influenced by any of the cytokines. The findings suggest that large changes in the SOD isoenzymes might occur in vascular diseases, significantly altering the susceptibility of the vascular wall to adverse effects of the superoxide radical.