In order to search for metals in the Lyman \alpha forest at redshifts z _ { abs } > 4 , we have obtained spectra of high signal-to-noise ratio and moderately high resolution of three QSOs at z _ { em } > 5.4 
discovered by the Sloan Digital Sky Survey .
These data allow us to probe to metal enrichment of the intergalactic medium at early times with higher sensitivity than previous studies .
We find 16 C IV absorption systems with column densities \log N { ( C~ { } IV ) } = 12.50 - 13.98 over a total redshift path \Delta X = 3.29 .
In the redshift interval z = 4.5 - 5.0 , where our statistics are most reliable , we deduce a comoving mass density of C ^ { 3 + } ions \Omega _ { C~ { } IV } = ( 4.3 \pm 2.5 ) \times 10 ^ { -8 } 
( 90 % confidence limits ) for absorption systems with \log N { ( C~ { } IV ) } \geq 13.0 ( for an Einstein-de Sitter cosmology with h = 0.65 ) .
This value of \Omega _ { C~ { } IV } is entirely consistent with those measured at z < 4 ; we confirm the earlier finding by Songaila ( 2001 ) that neither the column density distribution of C IV absorbers nor its integral show significant redshift evolution over a period of time which stretches from \sim 1.25 to \sim 4.5 Gyr after the big bang .
This somewhat surprising conclusion may be an indication that the intergalactic medium was enriched in metals at z \gg 5 , perhaps by the sources responsible for its reionization .
Alternatively , the C IV systems we see may be associated with outflows from massive star-forming galaxies at later times , while the truly intergalactic metals may reside in regions of the Lyman \alpha 
forest of lower density than those probed up to now .