Complex organisms use chemical signals, e.g., polypeptide hormones and growth factors, to integrate and coordinate the function of specialized tissues. Information is transferred to target cells when hormones bind to specific surface receptors and cell structure and function can be profoundly affected. We have developed a powerful experimental system (consisting of a giant, insulin-sensitive cell (amphibian oocyte), paraffin oil-based cell microinjection and fractionation procedures and single cell microanalysis) to study how such information flows to intracellular metabolic control prints, i.e., to define postreceptor signalling mechanisms. Recent research has focused on the role of intracellular receptors in the mechanism of insulin action. We have shown that microinjected, intracellular insulin stimulates both transcription and translation in oocytes by acting directly at nuclear and cytoplasmic sites. Moreover, insulin action at internal sites also occurs when cells are exposed to extracellular hormone, since the insulin-stimulated component of protein synthesis is partially blocked when cells are first exposed to external hormone and then microinjected with anti-insulin antibody. Future plans include: 1) defining the mechanisms by which insulin gains access to the internal receptors, 2) determining the extent to which intracellular receptors are involved in the action of polypeptide hormones and growth factors in oocytes and in somatic cells, 3) assessing the role of disrupted intracellular signalling in pathological states, e.g., insulin resistance, and 4) investigating the mechanisms of action of insulin mimics, e.g., vanadate and zinc.