We studied the effect of glucose starvation on glucose uptake and thymidine uptake and incorporation in cultures of normal chicken embryo cells and those transformed by Rous sarcoma virus. Resting normal fibroblasts increased the rate of glucose transport up to tenfold when they were starved for glucose, whereas fast-growing normal cells doubled the rate of uptake after starvation. Transformed cells did not show any change in the rate of glucose uptake during starvation. Thymidine uptake and incorporation by normal and transformed cells were not affected by glucose starvation. These results showed that a decrease in the glucose concentration of the medium induced a specific increase in the rate of glucose transport by normal chick fibroblasts, but did not change the transport of glucose by transformed cells. Therefore, it is suggested that glucose or one of its metabolic products regulated the hexose uptake of normal chick fibroblasts. Virus-transformed cells were insensitive to this regulation.