Total body composition of mice bearing Krebs-2 carcinoma transplanted subcutaneously was studied at several times during the course of tumor growth. Adult male Swiss mice, averaging 38 gm. in weight, sustained a profound fat loss during growth of Krebs-2 tumor. Fat depletion occurred in three stages. The first stage, involving loss of approximately 50 per cent of the lipide of the animal, occurred by 7 days after transplantation, before the tumor had reached appreciable size. The second phase was one of steady state in which no further fat loss occurred despite active tumor growth. This stage lasted approximately from day 7 to day 28. Premortally, the tumor-bearing animal lost another substantial quantity of fat.

The first stage fat loss has been reproduced with nonviable preparations from tumor. The possible nature of the lipolytic factor is discussed.

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Supported in part by a research grant from the United Fund of Erie County.

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