The euglycemic clamp technique has been widely used to examine changes in in vivo insulin sensitivity during physiological changes in mammals. The technique offers the advantage that the tissue uptake of glucose induced by a set dose of insulin is determined at the normal (steady state) circulating concentration of glucose (euglycemia). The euglycemic clamp technique has been modified to examine in vivo sensitivity to insulin in chickens. Insulin sensitivity is determined by the rate of infusion of exogenous glucose required to maintain euglycemia. Young (6 to 8-wk-old) male chickens (White Leghorn) are more sensitive to insulin than adult males of the same strain. There is, however, no difference in insulin sensitivity between young male chicks of broiler and White Leghorn strains. Chronic administration of beta-adrenergic agonist (L-640,033, donated by Merck, Sharp, and Dohme Research Laboratories, Rahway, NJ) in the diet, at levels of 0, .25, 1.0, and 4.0 ppm for 3 to 5 days also did not influence in vivo insulin sensitivity.