Abstract
This stock of albino mice is minimally inbred (0·5% per generation), and has been rigidly selected for fecundity. It is widely employed in oncological and pharmaceutical research. Spontaneous tumours arose in 55% of animals, multiple in 28%, averaging 1·66 per mouse. Females developed tumours at an earlier age than males. Predominant tumour types were pulmonary (23·1%), lymphoreticular (20%), and mammary (14%-23% of females). Miscellaneous tumour types (42·9%) ranged in frequency from 0·2 to 2·0%, the latter being hepatomas. Distribution of mammary tumours indicated that milk-borne mammary tumour virus was absent. Non-neoplastic disease was present in 58°6%, 24°1% being pulmonary and predominant in the young, while renal (31·2%) and cardiovascular (10·2%) disease was common in the elderly. Males outlived females.