  We examine rest-frame ultraviolet spectra of 70 high redshift quasars (z>3.5)
to study the chemical enrichment history of the gas closely related to the
quasars, and thereby estimate the epoch of first star formation. The fluxes of
several ultraviolet emission lines were investigated within the framework of
the most recent photoionization models to estimate the metallicity of the gas
associated with the high-z quasars. Standard photoionization parameters and the
assumption of secondary nitrogen enrichment indicate an average abundance of
Z/Z_sol = 4 to 5 in the line emitting gas. Assuming a time scale of t_evol =
0.5 - 0.8 Gyrs for the chemical enrichment of the gas, the first major star
formation for quasars with z>=4 should have started at a redshift of z_f = 6 -
8, corresponding to an age of the universe of several 10^8 yrs (H_o = 65
km/s/Mpc, Omega_M = 0.3, Omega_Lambda = 0.7). We note that this also appears to
be the era of re-ionization of the universe. Finally, there is some evidence
for a positive luminosity - metallicity relation in this high redshift quasar
sample.
