In the present study, we analyzed the activities of src and fyn tyrosine kinases and of protein tyrosine phosphatases (PTP), with particular interest to the striatal-enriched protein tyrosine phosphatase (STEP), in synaptosomal fractions prepared from the motor cortex and spinal cord of a transgenic mouse model of ALS (G93A mice), expressing wild-type human SOD1 (SOD1WT) or overexpressing human mutant SOD1 (SOD1G93A). The gene discussed is SRC; the disease is amyotrophic lateral sclerosis.