  The broad emission lines (BELs) of quasars and active galactic nuclei (AGNs)
are important diagnostics of the relative abundances and overall metallicity in
the gas. Here we present new theoretical predictions for several UV BELs. We
focus specifically on the relative nitrogen abundance as a metallicity
indicator, based on the expected secondary enrichment of nitrogen at
metallicities Z > 0.2 Z_o. Among the lines we consider, N III] 1750/O III]
1664, N V 1240/(C IV 1549 + O VI 1034) and N V/He II 1640 are the most robust
diagnostics. We argue, in particular, that the average N V BEL is not dominated
by scattered Ly-alpha photons from a broad absorption line wind. We then
compare our calculated line ratios with observations from the literature. The
results support earlier claims that the gas-phase metallicities near quasars
are typically near or several times above the solar value. We conclude that
quasar activity is preceded by, or coeval with, an episode of rapid and
extensive star formation in the surrounding galactic (or proto-galactic)
nuclei. Chemical evolution models of these environments suggest that, to reach
Z > Z_o in well-mixed interstellar gas, the star formation must have begun >
10^8 yr before the observed quasar activity.
