Associations with insulin resistance and islet beta-cell function have been studied cross-sectionally in a population-based sample of 4278 Mauritians comprising Asian Indian, Creole and Chinese subjects. Insulin resistance and beta-cell function were estimated by a computer solved model based on fasting plasma glucose and insulin concentrations. Insulin resistance increased with declining glucose tolerance, whereas beta-cell function was highest in subjects with impaired glucose tolerance (IGT) and lowest in those with non-insulin-dependent diabetes mellitus (NIDDM). Indian subjects had the highest beta-cell function, while ethnic differences in insulin sensitivity were less marked. This may indicate that deranged beta-cell function rather than insulin resistance is the primary determinant of hyperinsulinaemia and glucose intolerance in Asian Indians. beta-Cell function declined with age more sharply than did insulin sensitivity, suggesting that the age-related decline in glucose tolerance is primarily related to loss of beta-cell function. Body mass index, waist/hip ratio, physical inactivity and female sex were independently associated with insulin resistance and beta-cell function. Subjects with a family history of diabetes had increased insulin resistance, irrespective of glucose tolerance. This or similar models may have application in longitudinal population-based studies which seek to determine the relative contributions of insulin resistance and beta-cell function to the aetio-pathogenesis of NIDDM.