  We present detailed spectroscopic analysis of nitrogen abundances in 31
unevolved metal-poor stars analysed by spectral synthesis of the near-UV NH
band at 3360 A observed at high resolution with various telescopes. We found
that [N/Fe] scales with that of iron in the metallicity range -3.1 < [Fe/H] <0
with the slope 0.01+-0.02. Furthermore, we derive uniform and accurate (N/O)
ratios using oxygen abundances from near-UV OH lines obtained in our previous
studies. We find that a primary component of nitrogen is required to explain
the observations. The NH lines are discovered in the VLT/UVES spectra of the
very metal-poor subdwarfs G64-12 and LP815-43 indicating that these stars are N
rich. The results are compared with theoretical models and observations of
extragalactic HII regions and Damped Ly$\alpha$ systems. This is the first
direct comparison of the (N/O) ratios in these objects with those in Galactic
stars.
