Summary:Mice with catheters implanted in the jugular vein (infusions) and carotid artery (sampling) are used for this procedure (V3002). The hyperinsulinemic, euglycemic clamp or \u201cinsulin clamp\u201d has been used in a variety of species to assess insulin action. In an insulin clamp, the rate of glucose infused to maintain euglycemia is an index of whole body insulin sensitivity. Isotopes can be used during an insulin clamp to distinguish between insulin\u2019s effects on endogenous glucose production and glucose utilization, or to examine insulin\u2019s effects on specific tissues and metabolic pathways. The insulin infusion rate used in a study depends on a number of factors such as whether the experiment requires a sensitive analysis of endogenous glucose production, or whether the mouse is known to be unusually insulin resistant (e.g. ob\/ob). Finally the insulin clamp technique, especially when isotopes are involved, is most quantitative under steady state conditions. Therefore, clamps should be of a duration (~2 h) that is sufficient for the actions of insulin to obtain steady state. The section that follows describes, a) the technical procedures used on the day of a clamp experiment; b) preparation of insulin and tracer infusates; and c) analyses of plasma and tissue radioactivity. Familiarity with these procedures combined with laboratory demonstration provides the investigator with the necessary background to clamp the conscious mouse.