We have evaluated the G1H line of transgenic mice overexpressing a familial ALS mutation of SOD1 (Gly-93-->Ala) in tasks assessing different aspects of motor function to determine how early these deficits could be detected and their order of appearance. The earliest deficits were observed in tests of muscle strength and coordination as early as 8 weeks of age and their development appeared to be biphasic, whereas spontaneous activity was not impaired until 15 weeks of age. These studies show that, in addition to the previously demonstrated histological and electromyographic deficits, this transgenic mouse also presents changes in motor function reminiscent of the human disease, reinforcing and extending its validity as an animal model of familial amyotrophic lateral sclerosis (FALS) and allowing the investigation of novel drug treatment for ALS.