QUASARs are distant, luminous objects generally thought to be powered by the accretion of gas onto a supermassive black hole , their spectra are characterized by broad emission lines originating from a dense region close to the central energy source1. The best-studied spectral region in low-redshift quasars is near the Hbeta line at 4,861 angstrom (in the quasar rest frame) where there are also lines arising from singly ionized iron and doubly ionized oxygen. New technology has enabled us to detect strong iron emission in the spectra of the high-redshift (z > 3) quasars Q0014 + 813 and Q0663 + 680, in which these lines are redshifted to the near-infrared. The strength of this emission suggests an iron abundance (relative to hydrogen) higher than in the solar neighbourhood. This high iron abundance supports the view that quasars are located in the centres of massive galaxies. If type la supernovae are responsible for the iron enrichment2, significant star formation must have taken place in the host galaxies at least one billion years earlier, providing a constraint on the age of the Universe at that redshift.