D-[3H]mannoheptulose (or D-[1-14C] mannoheptulose) net uptake was measured in rat erythrocytes, parotid cells and hepatocytes. In the erythrocytes and parotid cells, the intracellular distribution space of the heptose (0.1 mM) represented only about 1 and 13%, respectively, of the intracellular 3HOH space. In hepatocytes, however, it amounted to approximately 45% of the intracellular 3HOH space. In all cases, the apparent distribution space of D-[3H]mannoheptulose hexaacetate largely exceeded that of unesterified D-[3H]mannoheptulose. Relative to the intracellular water space, the generation of acidic metabolites (expressed as an apparent distribution space) from radioactive D-mannoheptulose was one order of magnitude lower in parotid cells (< or = 3%) than in hepatocytes (> or = 20%). These findings are compatible with the hypothesis that D-mannoheptulose is transported into cells mainly, if not exclusively, at the intervention of GLUT2.