Mutations in the superoxide dismutase-1 (SOD1) gene occur in some forms of familial amyotrophic lateral sclerosis (ALS). To date about 150 mutations are known to involve this gene. Here we describe a novel missense mutation in exon 5 of the SOD1 gene in an Italian family with two members affected by ALS. Sequencing of the SOD1 gene was performed on 11 members of the family and 75 healthy controls. Electron microscopy was also performed on one ALS patient. We identified a heterozygous mutation in codon 137 leading to substitution of threonine by alanine. Further studies are needed to clarify the role of this alteration in ALS aetiopathogensis; nevertheless, T137A seems to represent a new missense mutation of the SOD1 gene in ALS patients.