Multiple peritubular nodules were found in the testes of three monkeys treated chronically with interstitial cell-stimulating gonadotrophins. The nodules were found persisting for as long as 7 months after injections had been discontinued. They were small, being visible only microscopically. The peripheral cells of the nodules merged imperceptibly with the surrounding intertubular tissue. Even where the interstitial cells were hypertrophic as well as hyperplastic, the cells of the nodules did not enlarge to form typical Leydig cells. The nodules appeared to be derived by proliferation of undifferentiated peritubular encapsulating cells. It is postulated that the cells of the nodules have a common origin with Leydig cells.

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This investigation was supported in part by research grants from the National Institutes of Health, Public Health Service, to Yale University School of Medicine and to the Institute of Experimental Biology, University of California; by grants from the Research Board of the University of California, and by grants from the Committee on Research, Council of Pharmacy and Chemistry, American Medical Association.

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