These studies describe key elements of the means through which the IL-4 receptor transduces functions of IL-4 and show relationships between these biochemical events and the major biological consequences of IL-4 action. In large measure, the control of IL-4-mediated growth and gene activation are segregated to different regions of the cytosolic domain of the receptor. These regions function by interacting with specific signaling molecules, leading to the activation of these molecules and the intracellular signaling pathways that result in the observed biological effects of IL-4.