1. The distribution of nuclear DNA values in the Lettré-Ehrlich mouse ascites carcinoma, and in some of its hypertetraploid (EL88) sublines, was studied by Feulgen cytophotometry. Metaphase chromosome counts were obtained from the same samples.

  2. In the Lettré-Ehrlich strain, the patterns of DNA distribution in the population and of chromosome number were constant and of the type expected from the work of others and from theoretical considerations.

  3. The EL88 sublines showed pronounced changes in DNA distribution and chromosome counts during the study. In addition, the DNA determinations revealed the presence of numbers of nuclei of polyploid DNA content, not apparent from chromosome counts.

  4. During subsequent culture of the EL88 sublines, the property of extensive polyploid production was lost from the population. After this shift, the pattern of DNA distribution was found consistent with that of the Lettré-Ehrlich strain.

  5. These findings are discussed in regard to the experimental use of ascites tumor populations.

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This study was supported by a research grant (C-1613C3) to Dr. Jack Schultz from the National Cancer Institute of the National Institutes of Health, U.S. Public Health Service, and an institutional grant from the American Cancer Society.

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