1. Increase in cytoplasmic granularity, used as one crtierion of toxicity in tissue culture screening of chemicals for selective toxicity to neoplastic cells, has been investigated. A variety of experimental conditions, including anoxia, could increase cytoplasmic lipid granularity in mouse fibroblasts in vitro.

  2. In mouse fibroblasts, increase in cytoplasmic lipid granularity and in plasmalogen could be inhibited or reversed for a limited time with serum albumin or by refeeding.

  3. In Sarcoma 180 cells, plasmalogen, but not the lipid granularity, was readily removable by means of serum albumin.

  4. Cells with massive lipid accumulations might not be unhealthy according to other criteria, including ability to proliferate.

  5. It is concluded that increase in cytoplasmic lipid granularity should be used only as a subsidiary indication of toxicity in the screening of chemical agents against neoplastic cells in culture.

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This work was supported in part by an institutional research grant from the American Cancer Society and was undertaken during the tenure of a Damon Runyon Memorial Fund grant. This investigation was supported in part by grant C-678 from the National Cancer Institute, of the National Institutes of Health, Public Health Service.

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