Species-related differences in the expression of selected proteins in pancreatic islet cells cannot be ignored. For instance, GLUT-2 was reported to be expressed at very low levels and not to be functionally essential in human ß cells. Likewise, whilst the expression of cystic fibrosis transmembrane conductance regulatory (CFTR) protein was documented in rat pancreatic islets by RT-PCR, Western blotting and imunocytochemistry, no conclusive evidence for the expression of CFTR in human islets was so far obtained. Such considerations led us to investigate in human pancreatic islets the expression of GLUT-2 and that of the electrogenic Na⁺- HCO₃^--cotransporter (NBCe1), recently documented by RT-PCR, Western blotting and immunocytochemistry in both rat pancreatic islets and tumoral insulin-producing BRIN-BD11 cells. GLUT-2 immunocytochemistry was compared in rat and human pancreatic sections. NBCe1 expression was investigated by RT-PCR in human islets and immunocytochemistry in human pancreatic sections. Immunostaining of GLUT-2 was comparable in human and normal rat islets. Expression of NBCe1 in islet cells was documented by RT-PCR in isolated human islets, and confirmed by immunocytochemistry of human pancreatic sections. The present findings argue, on one hand, against the view recently formulated that GLUT-2 expression is functionally not essential in human ß cells and, hence, too low to allow D-mannoheptulose entry into such cells. The fact already documented more than 40 years ago that the latter heptose inhibits insulin secretion in humans and the finding reported 10 years ago that tritiated D-mannoheptulose is indeed efficiently taken up by isolated human islets also argue against such a view. The observation that NBCe1 is well expressed in human islets warrants, on the other hand, further investigations on the participation of this cotransporter in the fluxes of bicarbonate anions in islet cells.