The effects of epinephrine and its precursors and metabolites on the iodine and intermediary metabolism of isolated calf thyroid cells were studied. Dopa, dopamine, and epinephrine, in increasing order of effectiveness, were stimulatory to iodine incorporation, iodothyronine synthesis, oxidation of glucose, synthesis of RNA from 3Huridine, and incorporation of mixed 14C—labeled amino acids into protein. The stimulatory response of these functions to dopa, dopamine, and epinephrine was also assessed in the presence of adrenergic blocking agents in concentrations which had no effect on these functions when added alone. Effects of iodine metabolism were inhibited by the alphaadrenergic blocker, phentolamine, but not the beta—blocker, propranolol. In contrast, stimulation of glucose metabolism was inhibited by both alphaand beta—adrenergic blockers, while stimulation of RNA synthesis and amino acid incorporation was inhibited by neither. It is suggested, therefore, that the isolated calf thyroid cell contains several separate adrenyl cyclase systems, with varying sensitivity to adrenergic blockers, and that biogenic amines may significantly affect the function of the thyroid cell in vivo. (Endocrinology92: 912, 1973)