Werner syndrome (WS) is a rare autosomal recessive disorder characterized by prematurely aged appearance. Genetic linkage analysis has placed the relevant gene in subchromosomal band 8p12. DNA polymerase beta gene has been mapped to chromosome 8p12-11 and thought to be involved in DNA repair and possibly in recombination. Somatic cells from WS patients exhibit chromosomal instability, a markedly reduced replicative life span and slow growth. The functions of DNA polymerase beta gene and its position prompted us to examine this gene in WS patients. We have found the novel DNA polymerase beta cDNA species in blood samples from WS patients, which contain 107 bp insertions or 87 bp deletions in the catalytic domain of DNA polymerase beta. These mutations change the structure of DNA polymerase beta and thus the capacity of the DNA repair system would be impaired, which may account for the high mutation rate observed in WS.