Experiments were carried out to investigate the extent of occurrence of a lactic dehydrogenase-augmenting agent in various types of tumors and its association with some known tumor-producing agents. It has been found that the agent was commonly associated with tumors which had been transplanted many times. Primary and transplanted tumors which were not exposed to exogenous sources of contamination did not show the presence of the agent. No association has been found between the agent and a variety of tumor-producing viruses. Lymphomas induced by Moloney virus showed the presence of the agent. However, tumors induced by the same virus, obtained from tissue culture, were free of the lactic dehydrogenase agent. The agent can be propagated and maintained apparently indefinitely by serial passages on primary mouse embryo tissue cultures.

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This investigation was initiated in the Department of Radiology, Stanford University School of Medicine, Palo Alto, California, and was supported in part by USPHS Grant CRT-5008 from the National Institutes of Health, Bethesda, Maryland.

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