Using the technic of Warburg, the carbohydrate metabolism of a series of lesions, associated with intra-cellular viruses has been examined. Where epithelial hyperplasia is evident (as in lesions of fowl pox in pigeons, vaccinia in young chickens, and human warts) an active metabolism is found, corresponding in type to that characteristic of malignant tissue, both qualitatively and quantitatively. When an active virus is present but unaccompanied by hyperplasia (as in the rain of guinea pigs dying of rabies), no deviation is found from the normal metabolism. The metabolic activity of fowl pox lesions shown graphically, exhibits a rough parallelism in its magnitude to the state of development or regression of the lesion. It is suggested that the magnitude and relationship of the respiratory and glycolytic processes, found by Warburg to be characteristic of malignant tissues, are not specific for malignancy but are a common feature of pathological overgrowths. Great variability in values for respiration in the Rous chicken sarcoma are recorded. Rous sarcoma cells, on their first appearance after injection of cell-free filtrate, assume the high metabolic activity characteristic of the fully grown tumor.