All subjects with eligibility will have had an oral glucose tolerance test performed within the past 3 months that revealed a normal fasting blood level and normal glucose tolerance. In addition, they will have had no history of significant cognitive disorders, no prior diagnosis of diabetes mellitus, and will not be receiving insulin or oral hypoglycemic. Eligibility for inclusion in the insulin-resistant group will be defined by scores on the Matsuda Index; non-insulin resistant controls will have normal values on the Matsuda Index. An effort will be made to ensure that both groups (i.e., those with insulin resistance and those without insulin resistance) will be similar in age, weight, BMI, and Apo E4 genotype (APOE).