Comparative studies of catalase activity in the liver, kidney, and erythrocytes of normal, cancerous, and protein-depleted rats were made. The results indicate:

  1. Liver catalase activity decrease is more severe in the case of Jensen rat sarcoma than in the UCLA fibrosarcoma. In many cases the UCLA fibrosarcoma grew to the same size as the Jensen sarcoma in the same time interval, with the liver catalase activity and erythrocyte volume closely approaching that of normal rats.

  2. In our experience with either tumor, liver catalase has not been below 20 per cent of the normal value. This is a less drastic effect than has been described in the literature.

  3. Kidney and erythrocyte catalase activity show small decreases, which may very well be within the experimental errors of the methods.

  4. Rats with growing tumors which suffer a loss in liver catalase also show an enlargement of the liver and the spleen and an increase in blood plasma. Cancerous rats with normal liver catalase activity show normal blood volumes and normal liver and spleen size.

  5. Rats kept on a protein-free diet suffer a drop in liver catalase activity to approximately 50 per cent of normal within 7–10 days from the time they were placed on the diet, and they remain at that level for 53 days or longer. When these animals are returned to a normal diet, the liver catalase activity returns to a normal value within 1–3 days, which is similar to the time required for recovery of tumor-bearing rats after extirpation of the tumor. Kidney catalase activity is slightly higher than normal, while erythrocyte catalase remains normal. Rats on a protein-free diet show no changes in blood volume or liver and spleen size.

  6. Evidence for the synthesis of catalase in tumor-bearing rats is shown by the UCLA fibrosarcoma by the constant erythrocyte volume maintained, with increasing total weight of the animal. The suggestion is made that the synthetic mechanism for liver catalase is probably not disturbed. The reduction in the catalase activity may be due to either a more rapid destruction of liver catalase or the abstraction from the blood stream of some necessary constituent by the tumor.

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This investigation was aided by a grant from the University of California cancer research funds.

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