Aldoses, ketoses, deoxy-aldoses, deoxy-keto-aldoses, lactones, deoxy-lactones and other similar compounds are readily reduced by NaBD, to the corresponding polyalcohol. Their trimethylsilyl ethers show characteristic mass spectra which allow firm assignments of the position of deuteration and hence of the nature of the starting sugar compound. The g.c./m.s. coupling technique even allows trace analysis since full information can be derived from the most intense fragments of the mass spectra.