Detailed reference data are given for survival and for all types of neo-plastic lesions found in inbred NZO/B1 mice from the original colonies. NZO/B1 mice are unusual in producing malignant lymphomas of Peyer's patches, and a high incidence of duodenal and lung tumours. They are very responsive to most chemical carcinogens. The significance generally of the data is briefly discussed, and reference statistics for neoplasms with more than 1% incidence in untreated animals are tabulated to assist other laboratories studying NZO/B1 mice.

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N-nitrosododecamethyleneimine ( N D M I ) , a new member of the alicyclic nitroso imine series, was synthetized and tested in NZOIBI mice, as part of structure-activity studies. Treated mice had signiJcant incidences of liver and glandular stomach tumors, thought to represent the characteristic oncogenic activity of NDMI. There were also statistically signiJcant increases in tumors of lung, duodenum and reticular tissues, but these tumors were common in controls. By contrast with the strong carcinogenic activity of lower members of the series towards pharynx and esophagus, NDMI produced no lesions at these sites. A synthesis for NDMI is given.

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