The genetically obese Zucker rats (fa/fa) represent a model of insulin resistance and prediabetes characterized by hyperinsulinemia, hyperlipidemia and peripheral glucose intolerance which is caused largely by an impairment of insulin-stimulated glucose uptake into skeletal muscle, the major site of insulin-mediated glucose disposal (Ionescu et al., 1985; King et al., 1992). The gene discussed is INS; the disease is hyperinsulinism.