For short-term carcinogenesis experirnents using animals, a method studying the incidence of pulmonary adenoma in newborn mice has been generally adopted, but this method still needs mote than 24 weeks. This expenment is one of the attempts to make such experiment period shorter. In this experimeit, both'inbred mice such as C57BL/6J, C57BR/cdJ, A/J strain and non- inbred NIH(GP) strain were used. Each mouse group was sacrificed nine weeks after a single injection of benzo(a)pyrene into subscapular region within 24 hours after birth. In C57BL/6J or C57BR/cdJ mice, no pulmonary adenoma was observed at either normal control group or bepzo(a)pyrene-injected groups by 0. 5 mg or I mg. In A/J inbred mice, however, the incidences of pulmonary adenoma were 3.9 per cent at normal control group, 86,7 per cent at 0.5 mg benzo(a)pyreae group and 88. 3 per cent at I mg benzo(a)pyrene group, respectively. In non-inbred NiH(GP) mice, the incidences were 2.5 per cent at normal group, 46. 8 per cent at 0. 5 mg group and 54. 4 per cent at 1 mg group, respectively. To verify he utility of this experiment, an NIH(GP) newborn mouse group, after inje- ction of 500 pw of benzo(a)pyrene, was administered ascorbric acid through drinking water for six weeks after they were weaned. it was observed that the pulmonary adenoma incidence was 46.8 per cent at the group injected 500 ug of benzo(a)pyrene only wbile it was decreased to 29. 5 per cent at the group administered both SQl pg of benso(a)pyrene and ascorbic acid, thus showed 37 per cent of the Prevention effect. It was proved from the above result that this method was useful to detect anticarcinogenes.
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