The glucose metabolism and the related intracellular processes of Tetrahymena pyriformis GL cells are measurably influenced by several hormones of higher organisms, among others by the endocytosis stimulating hormone histamine, and the glucose metabolism regulating hormone insulin. Histamine does not interfere with the glucose metabolizing action of insulin, but markedly enhances the utilization of glucose, to judge from a significant decrease in the PAS-positive (hexose) component of histamine-exposed Tetrahymena pyriformis GL cells.