Summary of work in progress includes the following: 1) A further definition of the X-ray induced G2 block in terms of effects on specific chromosomal proteins and possible ultrastructural changes will be continued; 2) The mutation frequency as a function of radiation dose will be examined more closely in terms of the true shape of the curve. Specifically, we are determining if the spectrum of mutants as determined by resistance to different concentrations of 8-azaguanine is the same throughout the cell cycle and for different radiation doses; 3) The kinetics of repair of thermal lesions for different temperatures will also be determined with lethality and possible chromosomal aberrations as the end point. Also, effects of hypoxia on the hyperthermic radiosensitization will be studied; 4) Experiments will be continued to determine whether or not X-rays indeed have an effect on the attachment of DNA to the nuclear membrane. BIBLIOGRAPHIC REFERENCES: L.E. Hopwood, W.C. Dewey, and W. Hejny: "Transport of thymidine during the cell cycle in mitotically synchronized CHO cells." Exp. Cell Res. 96: 425-429 (1975). Donald E. Thrall, Leo E. Gerweck, E.L. Gillette, and William C. Dewey: "Effects of heat, both alone and in combination with X-rays, in vivo and in vitro." In: Advances in Radiation Biology, Vol. 9, J. Lett, M. Zelle, and H. Adler (eds), Academic Press, New York, New York (1976).