A novel mutation, a C-->T transition at nucleotide 455 of the coding sequence of the ARSA gene, was found in a control individual during the search for metachromatic leukodystrophy mutations. Its distribution in three different populations was examined. The frequency of the T allele was 0.058, 0.025 and 0.033, in Italian, German and Greek populations, respectively. The mutation results in no amino acid substitution and can be identified as it creates a a polymorphic site for the restriction endonuclease N/aIII.