D/H observations in the interstellar medium

Evaluations of the primordial deuterium abundance should provide one of the best tests of big bang nucleosynthesis models. Observations in different astrophysical sites were made in order to link present day interstellar medium D/H evaluations to primordial ones. The evaluations in the interstellar medium are presented with special emphasis on the observations done in the ultraviolet. The outcome of these observations seems to indicate that no variation of the deuterium abundance is seen within 100 pc and leading to an average value (D/H)=1.4 (±0.24)×10−5. D/H variations are, however, detected on larger scales. The consequences are briefly discussed.