We have introduced the beta 2-adrenergic receptor into the unnatural environment of a thyroid cell to demonstrate that the activation of this receptor initiates diverse cellular programs in different cell types. The thyroid-stimulating hormone (TSH) receptor and the beta 2-adrenergic receptor stimulate a common signaling pathway in distinct populations of cells. In this study, we demonstrate that the activation of the beta 2-adrenergic receptor, transfected into a thyroid epithelial cell, elicits a program of growth and differentiation normally observed with TSH. In thyroid cells expressing beta 2 receptors, the beta 2 agonist isoproterenol activates adenylate cyclase, induces the expression of a thyroid-specific iodide carrier system, and can substitute for TSH to promote growth. Thus, in thyroid cells expressing beta 2-adrenergic receptors, isoproterenol elicits the entire array of thyroid-specific functions normally activated by TSH.