The main function of the islet of Langerhans is the control of glucose homeostasis. Several types of endocrine cells, mainly alpha-, beta- and delta-cells, respond to changes in extracellular glucose concentrations with the release of glucagon, insulin and somatostatin, respectively. In the pancreatic beta-cell, the model for the stimulus-secretion coupling is currently accepted, and implies a key role for mitochondrial function. Extracellular glucose elevations trigger mitochondrial metabolism, activating the tricarboxylic acid cycle, and thereby increasing the concentration of redox electron carrier molecules, which stimulate oxidative phosphorylation and ATP synthesis. The increase in ATP/ADP ratio inhibits ATP-dependent K⁺ channels, leading to a depolarization-induced Ca²⁺ signal that triggers insulin release. In contrast, little is known in alpha- and delta-cells about the metabolic responses involved in the signalling pathways that lead to secretion. This lack of information is mainly due to the scarcity of non-beta-cells in the islet and certain limitations of conventional methods. In the present research, we monitored the fluorescence of either flavoproteins or NAD/NADH by redox confocal microscopy to analyse the mitochondrial metabolic responses to glucose of individual alpha-, beta- and delta-cells in fresh intact islets (Quesada et al. 2006). Activation of mitochondrial metabolism leads to a decrease in the fluorescence of flavoproteins. The percentage of decrease was calculated as the change in fluorescence from the signal obtained with 0.5 mM glucose. Data were expressed as means ± SEM. Statistical significance was analysed using a Student’s t test (p<0.05). All cases were found significant. After recording autofluorescence in single cells within the islet, we performed immunochemical protocols to identify the different cell types in the same optical slice (Quesada et al. 2006). Pancreatic beta-cells responded with a homogeneous dose-dependent metabolic pattern from 0.5 to 25 mM glucose. At 25 mM glucose, the fluorescence decreased 34.11 ± 2.16% (n=45 cells). Delta-cells exhibited a similar pattern although the response was about 3-fold lower (10.41 ± 2.54% at 25 mM glucose, n=13 cells) than beta-cells. However, glucose produced minor or no effect in the fluorescence of alpha-cells (2.88 ± 0.69% at 25 mM glucose, n=36 cells), despite their metabolism being sensitive to drugs acting on mitochondrial function. After autofluorescence records, these cells were able to develop Ca²⁺ signals, indicating their normal function. Similar results were obtained in cultures of dispersed cells. These observations indicate important metabolic differences in glucose utilisation among alpha-, beta- and delta-cells, and further indicate divergences in the signalling pathways that lead to hormone release in each cell type.