THE abnormal assembly and accumulation of neurofilaments (NF) in the perikarya and proximal axons of motor neurones is a characteristic of ALS. Deletions in the KSP repeat region of theNF-Hgene have previously been reported in seven patients with sporadic ALS. Here we report the identification of a novel 84bp insertion in theNF-Hgene. This leads to an extra four KSP repeat elements in a highly conserved repetitive region of the gene. Although neurofilament mutations are only associated with a very small proportion of ALS cases, this insertion provides further support of a role for neurofilaments in the pathogenesis of ALS.