Sensitivity of pancreatic islets to hypoxia is one of the most important of the obstacles responsible for their failure to survive within the recipients. The aim of this study was to compare the in vitro hypoxia tolerance of neonatal and adult rat islet cells and to study the glucose metabolism in these cells after exposure to hypoxia. Islet cells from both age categories were cultured in different hypoxic levels for 24 h and insulin secretion and some metabolites of glucose metabolism were analysed. Glucose-stimulated insulin secretion decreased dramatically in both cell preparations in response to the decrease in oxygen level. The reduction of insulin secretion was more detectable in adult cells and started at 5% O(2), while a significant reduction was obtained at 1% O(2) in neonatal cells. Moreover, basal insulin release of neonatal cells showed an adaptation to hypoxia after a 4-day culture in hypoxia. Intracellular pyruvate was higher in neonatal cells than in adult ones, while no difference in lactate level was observed between them. Similar results to that of pyruvate were observed for adenosine triphosphate (ATP) and the second messenger cyclic adenosine monophosphate (cAMP). The study reveals that neonatal rat islet cells are more hypoxia-tolerant than the adult ones. The most obvious metabolic observation was that both pyruvate and lactate were actively produced in neonatal cells, while adult cells depended mainly on lactate production as an end-product of glycolysis, indicating a more enhanced metabolic flexibility of neonatal cells to utilize the available oxygen and, at the same time, maintain metabolism anaerobically.