Most sera from 26 chickens hatched and reared in isolation and showing an absence or a low incidence of lymphomatosis were devoid of neutralizing antibodies for the Rous sarcoma virus. Most sera from 24 genetically related chickens reared in contaminated surroundings, and showing a high incidence of lymphomatosis, did show the neutralizing antibodies.

Suggestive, though not entirely conclusive, evidence of a relationship between lymphomatosis and Rous sarcoma viruses was obtained from experiments designed to test the hypothesis that the two agents possess common antigens.

The results are discussed from the point of view of the origin of tumor viruses, and also from the point of view of a possible derivation of sarcoma viruses from the viruses of lymphomatosis through a process of variation.

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This investigation was aided by grants from the Jane Coffin Childs Memorial Fund for Medical Research, the American Cancer Society, and the National Cancer Institute, National Institutes of Health, U.S. Public Health Service.

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