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The paper discusses the incidence of spontaneous tumors and general morbidity in albino noninbred rats raised at the N. N. Petrov Research Institute of Oncology of the USSR Ministry of Health and used in different chronic experiments. It was found that spontaneous tumors occur, on the average, in 25.7 and malignancies--in 6.2%. Infectious hemorrhagic pneumonia and gastroenteritis (acute capillary toxicosis) are relatively infrequent. The general morbidity patterns in these rats are similar to those in Wistar line, the essential difference being a lower frequency of tumors of the medullar layer of adrenals. Hence, the rats bred at the Institute may be successfully used in various chronic experiments, including those associated with carcinogenic studies.

Data obtained from the 10 year study of the spontaneous neoplasm incidence in mongrel mice and rats (males and females) from the colony of the R.E. Kavetskiĭ Institute for Oncology Problems are adduced. Spontaneous carcinogenesis was at an average 1:8 in mice (132 tumours per 1120 mice) and 1:3 in rats (93 tumours per 335 rats). Tumours of mammary glands and of pituitary prevailed in rat females.