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Transplantation of pancreatic islets is efficient in improving the metabolic control and quality of life and in preventing severe hypoglycemia in patients with brittle type 1 diabetes mellitus. More accurate methods to assess islet viability would be extremely useful in designing target interventions for islet cytoprotection and in reducing the number of islets required to achieve insulin independence. Here we report on an application of calorimetry to evaluate the metabolic response of pancreatic islets to glucose stimulation. A significant increase in metabolic heat was produced by islet samples when consecutively subjected to 2.8 and 16.3 mmol L −1 glucose. Under these glucose concentrations, 1000 islets released average heat values of 9.16 ± 0.71 mJ and 14.90 ± 1.21 mJ over 50 min, respectively. Additionally, the glucose stimulation indexes were 1.67 ± 0.30 for insulin, 1.72 ± 0.13 for heat and 2.91 ± 0.50 for lactate, raising the important possibility of substituting the secreted insulin index/ratio by the index/ratio of the heat released in the evaluation of Langerhans islets viability for transplantation. Altogether, our results demonstrate the applicability of calorimetry to assess the quality of isolated pancreatic islets and to study vital islet functions.