D-mannoheptulose is apparently transported into cells mainly at the intervention of GLUT-2 and hence was recently proposed as a tool to label preferentially insulin-producing -cells in the pancreatic gland. The validity of such a proposal was investigated in the present study conducted in isolated perfused pancreatic glands from control and streptozotocin-induced diabetic rats. After a 30-min equilibration period, D-[³H]mannoheptulose (0.1 mM) and [U-¹⁴C]sucrose (0.5 mM) were infused for 15 min in the presence of 30 mM D-glucose. The pancreatic glands were then perfused for 10 min with a nonradioactive medium during and after administration of cytochalasin B (0.02 mM). Under these experimental conditions, the intracellular distribution space of D-[³H]mannoheptulose averaged 5.42 ± 0.75 nl/mg in control animals, whereas it failed to be significantly different from zero in the streptozotocin rats. The present procedure may thus allow the assessment of the relative contribution of islet -cells to the total mass of the pancreatic gland.