1. The effect of 8-methoxypsoralen upon ultraviolet skin carcinogenesis in mice has been studied. This compound produces an increased photosensitivity of the skin, and also absorbs strongly in the ultraviolet wavelengths. Swiss mice were exposed to the total irradiation from ultraviolet lamps for 15 minutes per day. 8-Methoxypsoralen was administered in the diet or intraperitoneally.

  2. The final incidence of ear tumors in mice receiving dietary 8-methoxypsoralen was considerably less than that of the controls. The extent of protection afforded by this compound appeared to be proportional to its concentration in the diet, up to an optimal level.

  3. Those mice receiving intraperitoneal injections of 8-methoxypsoralen 1 hour prior to ultraviolet exposure exhibited early severe erythema. The final ear tumor incidence was nearly 100 per cent, as compared with 68 per cent in the control group. An accelerated latent period of carcinogenesis was also observed. If the compound was administered 20 hours before irradiation, the final ear tumor incidence was in the same range as that of the controls.

  4. These findings are discussed with respect to wave length, erythemal response, dose level, and time of administration of the compounds.

*

A preliminary report of these findings was presented at the annual meeting of the American Association for Cancer Research, Atlantic City, New Jersey, April, 1956.

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