  (Abridged) Estimates of the interstellar deuterium abundance span a wide
range of values. Here we study the evolution of deuterium in the framework of
successful models for the chemical evolution of the Milky Way able to reproduce
the majority of the observational constraints for the solar neighbourhood and
for the Galactic disc. We show that, in the framework of our models, the lowest
D/H values observed locally cannot be explained in terms of simple astration
processes occurring during the Galaxy evolution. Indeed, the combination of a
mild star formation and a continuous infall of unprocessed gas required to fit
all the available observational data allows only a modest variation of the
deuterium abundance from its primordial value.
