Abstract
In recent years, multiply deuterated molecular species have been detected towards many protostellar sources with abundances much higher than the cosmic abundance of deuterium would suggest. These results still pose somewhat of a challenge for the chemical models of the ISM, but might bring very important new clues about the chemical evolution of protostars, particularly about the chemical interplay between dust and gas in those objects. A proper understanding of this gas--grain interplay will only be obtained by combining spectroscopic millimetric observations of the gas with spectroscopic infrared observations of the dust-grain contents.
