  Aims. The aim of this work is to compare the detailed chemical composition of
the field N-rich dwarf stars to the second generation stars of globular
clusters (GC) in order to investigate the hypothesis that they originated in
GCs. Methods. We have measured the abundance of 23 elements (from Li to Eu) in
a sample of six metal-poor N-rich stars (three of them pointed out for the
first time) and we have compared their chemical composition to, (i) the
chemical composition observed in a sample of classical metal-poor stars, and
(ii) the abundances observed in the second generation stars of GCs. Results. In
metal-poor N-rich stars C and O are slightly deficient but the scatter of
[(C+N+O)/Fe] is very small, a strong indication that the N enrichment is the
result of a pollution by CNO processed material. The N-rich stars of our
sample, like the second generation stars in the GCs, show an excess of Na and
sometimes of Al, as expected if the material from which these stars were
formed, has been polluted by the ejecta of massive AGB stars. For the first
time we have been able to establish an anti-correlation Na-O in field stars
like the one observed in NGC6752. The N-rich star HD 74000 has a rather low
[Eu/Ba] ratio for its metallicity. Such an anomaly is also observed in several
second generation stars of M15. Conclusions. This analysis supports the
hypothesis that the N-rich stars today observed in the field, were born as
second generation stars in GCs.
