The human progeroid disorders Cockayne syndrome and Werner syndrome present with several clinical features that are associated with normal aging. These include distinct changes in the skin. The genes responsible for these conditions have recently been cloned and characterized. They both contain a characteristic helicase sequence, and helicase activity has been demonstrated using the purified Werner protein. Helicases are involved in a number of DNA metabolic transactions, including transcription, replication, and DNA repair. Cockayne cells are deficient in a special type of DNA repair, transcription coupled DNA repair, but they also appear to be defective in basal transcription. The diverse functions of the Cockayne protein are under intense study. Werner cells may have subtle defects in DNA repair, and possibly also in transcription. The biochemical clarification of the precise role of these gene products is likely to provide very significant clues into the mechanism of aging.