1. A 12.7 per cent incidence of fibrosarcoma was found in rats with polyethylene implants. No tumors were found in a control group which received similar surgical treatment but in which no polyethylene implant was made.

  2. Sex was not a factor in the production of tumors by polyethylene.

  3. The tumors occurred both with implants in the abdominal wall and over the skull.

  4. The polyethylene implants did not affect the incidence of breast tumors in females.

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This work has been supported by research grants 3369 and 3369(C) from the National Institutes of Health, Public Health Service.

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