Twenty blood samples from Russian patients (Moscow) with idiopathic motor neurone disease were analysed for mutations in the Cu,Zn superoxide dismutase (Cu,Zn SOD) gene. Two patients (10%) with the amyotrophic lateral sclerosis (ALS) form of the disease were found to have a disease-related mutation. One patient appears to have autosomal recessive adult-onset ALS associated with homozygosity for D90A and presents the characteristic phenotype of very slowly ascending paresis with both lower and upper motor neurone signs. Another patient, heterozygous for D90A, presents ALS with lumbar onset and rapid progression. This is the first report of a Cu,Zn SOD mutation in ALS in Russia.