To elucidate the nature of chemical and physical damage to DNA by means of mammalian corrective endonuclease. To investigate the repair capacity of cells of individuals with congenital syndromes associated with increased incidence of malignancy. To purify distinct mammalian corrective endonucleases. BIBLIOGRAPHIC REFERENCES: Teebor, G. W. and Duker, N. J. Human endonuclease activity for DNA apurinic sites. Nature, 258:544-547, 1975.