This is an epidemiologic prospective study which proposes to follow-up a subgroup of individuals from the San Antonio Heart Study (a population-based survey) who have impaired glucose tolerance and study their conversion to non-insulin dependent diabetes mellitus (NIDDM); subjects with IGT are estimated to have a four-fold increased risk of NIDDM. Our sample consists of Mexican Americans and Anglos; the former has been shown to have a much higher prevalence of NIDDM as well as an apparent increased risk of NIDDM over Anglos even after controlling for known risk factors such as obesity, indicating a possible genetic component of the diease. By following subjects who have IGT, we will estimate their conversion rates and examine potential risk factors for conversion, including measures of adiposity, demographics, metabolism (e.g., plasma insulin), diet, and genetic predisposition (including genetic markers and admixture). These will be analyzed both univariately and multivariately. Identification of predictors of conversion may (1) allow the early identification of those at high risk of NIDDM in order to intervene in the course of the disease, and (2) further the understanding of the etiologies of NIDDM, including assisting in the identificaton of the presence of a major gene for NIDDM.