  The intensity of the strong N V 1240 line relative to C IV 1549 or to He II
1640 has been proposed as an indicator of the metallicity of QSO broad emission
line regions, allowing abundance measurements in a large number of QSOs out to
the highest redshifts. Previously, it had been shown that the (normally) much
weaker lines N III] 1750 and N IV] 1486 could be used in the same way. The
redshift 1.96 QSO 0353-383 has long been known to have N III] and N IV] lines
that are far stronger relative to Ly-alpha or C IV than in any other QSO.
Because in this particular case these intercombination lines can be easily
measured, this unusual object provides an ideal opportunity for testing whether
the N V line is a valid abundance indicator. Using new observations of
Q0353-383 made both with HST in the ultraviolet and from the ground in the
visible passband, we find that intensity ratios involving the strengths of N V,
N IV] and N III] relative to lines of He, C and O all indicate that nitrogen is
overabundant relative to oxygen in Q0353-383 by a factor of ~15 compared to
solar ratios. This agreement among the diagnostics supports the use of these
lines for measuring BLR chemical abundances. If nitrogen behaves like a
secondary element, such that N/O is proportional to O/H, then the extreme
nitrogen enhancement in Q0353-383 implies a metallicity of ~15 times the solar
value. Even if Q0353-383 represents an extreme outlier in the N/O proportional
to O/H relation, the overall metallicity should still be at least five times
solar. Unusually high metallicities in Q0353-383 might imply that we caught
this object just as the gas-phase metallicity in the central part of its host
galaxy has peaked, at a time when the interstellar gas supply is nearly
exhausted and hence the fuel source for the central QSO is ready to shut off.
