In the 9-day cultures of liver cells isolated from newborn rats epinephrine was found to increase the number of glycogen containing cells, and caused an elevation of the glycogen content of individual liver cells. Insulin treatment had a weak effect on the number of glycogen containing cells and its effect on intracellular glycogen content was negligible. The experiments indicate that the epinephrine receptor develops in the fetal period and is reactive in the newborn animal, while the insulin receptor is not. It was remarkable that in this period of life and under in vitro conditions the effect on cellular glycogen deposition of epinephrine and insulin is similar.