The histochemical analysis of succinic dehydrogenase by means of a tetrazolium salt in azo dye-induced rat liver hepatoma has revealed the existence of two types of malignant cells, which have different histochemical patterns. The lower level of succinic dehydrogenase previously found by many authors in similar hepatoma by homogenate technic can be explained as an index of an average of general succinic dehydrogenase activity in a tissue, where part of the cells contain a fairly normal amount of this enzyme and part none at all.

In this series of azo dye-induced tumors we were unable with this histochemical technic to distinguish between benign and malignant cells.

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This investigation was supported in part by research grant number C-2624 from the National Cancer Institute, U.S. Department of Health, Education, and Welfare, and in part by an Institutional Grant from the American Cancer Society.

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