The study population was selected to insure adequate numbers of participants within gender and glucose tolerance groups (normoglycemia, impaired glucose tolerance, and non-insulin dependent diabetes mellitus). IRAS is the first large epidemiologic study to include detailed measurements of insulin sensitivity and secretion. During the first four years of funding, the IRAS investigators successfully designed and implemented the first phase of the study--a cross-sectional evaluation of 1,625 participants. Cohort examinations began in October, 1992 and were completed in April, 1994. Insulin resistance was assessed directly using the frequently sampled intravenous glucose tolerance test with minimal model analysis. Intimal-medial carotid artery wall thickness, an indicator of atherosclerosis, was measured using B-mode ultrasonography. Prevalent cardiovascular disease was assesed by questionnaire and resting electrocardiography.