  We report on a survey of \nh2d towards protostellar cores in low-mass star
formation and quiescent regions in the Galaxy. Twenty-three out of thirty-two
observed sources have significant ($\gsim 5\sigma$) \nh2d emission.
Ion-molecule chemistry, which preferentially enhances deuterium in molecules
above its cosmological value of \scnot{1.6}{-5} sufficiently explains these
abundances. NH2D/NH3 ratios towards Class 0 sources yields information about
the ``fossil remnants'' from the era prior to the onset of core collapse and
star formation. We compare our observations with predictions of gas-phase
chemical networks.
