MEANS of distinguishing between enantiomers of a chiral molecule are of critical importance in many areas of analytical chemistry and biotechnology, particularly in drug design and synthesis. In particular, solution-based sensor systems capable of chiral recognition would be of tremendous pharmaceutical value. Here we report the chiral discrimination of D- and L -monosaccharides using a designed receptor molecule that acts as a sensor by virtue of its fluorescent response to binding of the guest species. Our receptor contains boronic acid groups that bind saccharides by covalent interactions; such receptor systems have been much studied previously1–6 for complexation of saccharides, and have an advantage over others based on hydrogen-bonding interactions7–11, for which polar protic solvents such as water can compete with guest binding. Our molecular sensor also incorporates a fluorescent naphthyl moiety; binding of each enantiomer of the monosaccharides alters the fluorescence intensity to differing degrees, enabling them to be distinguished. These water-soluble molecular sensors might form the basis of a quantitative and selective analytical method for saccharides.