THE anomers α- and β-D-mannose differ structurally only in that H and OH at the C1 atom of the pyranose ring are interchanged. In spite of this apparently minor difference in structure, it has been suggested that the ambiguity of taste perception of D-mannose is due to actual differences in taste between the two anomers of this substance; the evidence presented in support of this view, however, was indirect because insufficient pure β-D-mannose was available for direct taste tests on that anomer1. Sufficient pure β-D-mannose was therefore prepared for a direct and statistically reliable comparison. It was found that the subjects reliably reported the α-anomer as sweet and the β-anomer as bitter. As before, the equilibrium mixture was found to be an ambiguous stimulator.