Abstract Gene mutations of Cu/Zn superoxide dismutase (SOD) have been discovered in familial amyotrophic lateral sclerosis (ALS). Oxidative stress also plays a role in the pathogenesis of sporadic ALS. Whether antioxidant therapy is beneficial in this fatal disease is now crucial. We have shown that SOD treatment improves neuromuscular dysfunction and morphological changes in wobbler mouse motoneuron disease. Progressive spinal motor neuronopathy and axonopathy, predominantly in the cervical cord, occur at postnatal age 3–4 weeks, leading to muscle weakness and contracture of the forelimbs in this animal. These motor deficits rapidly increase by postnatal age 6–8 weeks, and then slowly progress. Wobbler mice were given two doses daily of phosphatidyl choline-bound Cu/Zn SOD (PC-SOD, 10 4, 10 5 U/kg) or a vehicle solution by intraperitoneal injection from postnatal 3–4 to postnatal 7–8 weeks of age. PC-SOD treatment attenuated progression of motor dysfunction, prevented denervation muscle atrophy, and delayed degeneration of spinal motoneurons in wobbler mice. This raises the possibility that PC-SOD may have therapeutic potential in human motoneuron disease.