Prostaglandins (PGs) are critical mediators of physiologic processes and inflammation. They are produced by two different isoforms of the cyclooxygenase (COX) enzyme, namely COX-1 and COX-2. In particular COX-2 was demonstrated to be crucial for PG-synthesis in inflammation. Recently, inhibition of COX-2 was shown to prevent the loss of motor neurons in a model of amyotrophic lateral sclerosis (ALS). Furthermore, spinal COX-2 expression was shown to be increased in transgenic mice that produce an ALS–like syndrome. Therefore, we investigated the expression of COX-1 and COX-2 in the spinal cord of seven human sporadic ALS patients by means of immunohistochemistry. Specimens from seven patients without any neurological disease served as controls. COX-2 expression was dramatically increased in the spinal cord of patients with ALS. Its protein was found in motor neurons, interneurons and glial cells. Statistical analysis showed a significantly higher expression of COX-2 in ALS for both neurons and glia. In contrast, COX-1 expression was predominantly confined to microglia and no apparent difference was detected between controls and ALS. In addition, we studied the concentration of prostaglandin E2 (PG E2) as a marker for COX activity in the cerebrospinal fluid of nine patients diagnosed for ALS and compared the results with those from nine patients without motor neuron disease. PG E2 levels were markedly increased in ALS cases (45.8 ± 35.1 pg/mL) compared to the non-ALS specimens (15.8 ± 3.7 pg/mL). The results of our study corroborate a potential role for COX-2 in the pathogenesis of motor neuron death in ALS. Selective COX-2 inhibition might therefore offer a new possibility in the treatment of human ALS. However, to determine the exact role of COX-2 in human ALS will require further research.