Werner's syndrome (WRN) is a rare autosomal recessive disorder characterized by the appearance of features of premature aging in a young adult. Skin fibroblasts from WRN patient demonstrate slow growth, reduced life span in vitro and mutator phenotype. The genetic defect in WRN is unknown. We have studied 23 WRN patients mainly from first or second cousin marriage and have applied homozygosity mapping to search for the WRN locus. A peak lod score of 5.58 at a recombination fraction of 0.03 was obtained with D8S87. We confirmed that the WRN locus was located on the short arm of chromosome 8, 8p11.2-p12.