Mutations in the copper/zinc superoxide dismutase (mSOD1) gene are associated with a familial form of amyotrophic lateral sclerosis (ALS), and their expression in transgenic mice produces an ALS-like syndrome. Recent observations suggest a role for inflammatory-related events in the progression and propagation of the neurodegenerative process in ALS. Consistent with this view, the present study demonstrates that, during the course of the disease, the expression of cyclooxygenase type 2 (Cox-2), a key enzyme in the synthesis of prostanoids, which are potent mediators of inflammation, is dramatically increased. In both early symptomatic and end-stage transgenic mSOD1 mice, neurons and, to a lesser extent, glial cells in the anterior horn of the spinal cord exhibit robust Cox-2 immunoreactivity. Cox-2 mRNA and protein levels and catalytic activity are also significantly increased in the spinal cord of the transgenic mSOD1 mice. The time course of the spinal cord Cox-2 upregulation parallels that of motor neuronal loss in transgenic mSOD1 mice. We also show that Cox-2 activity is dramatically increased in postmortem spinal cord samples from sporadic ALS patients. We speculate that Cox-2 upregulation, through its pivotal role in inflammation, is instrumental in the ALS neurodegenerative process and that Cox-2 inhibition may be a valuable therapeutic avenue for the treatment of ALS.