Insulin resistance was evaluated in South American camelids, llamas and alpacas, by use of the minimal model test and the insulin tolerance test. Animals were catheterized for long-term studies and tamed to minimize stress during evaluation. Results indicated a low insulin sensitivity index (SI) = 0 to 0.97, median = 0.39 x 10(-4) min/uIU x ml, about a fifth the value in other mammals and humans. The KITT was between 1.43 and 3.19 %/min, also significantly lower than that reported for humans. Glycosylated hemoglobin concentration was 6%, and HbAlc concentration was 5.5%; red blood cell lifetime, as measured by use of the 51Cr method, was 120 days, similar to the value in humans. We concluded that llamas and alpacas have naturally higher blood glucose concentration than do humans and other mammals during the glucose tolerance test. Using the same mathematical tools to evaluate glucose metabolism as those used in people, South American camelids appear to be resistant to insulin. Thus, the South American camelid may be a useful new animal model for the study of sugar metabolism and various facets of diabetes mellitus, especially protection from the deleterious effects of glycosylation.