  We present J-H-K' photometry for a sample of 45 high redshift quasars found
by the Sloan Digital Sky Survey. The sample was originally selected on the
basis of optical colors and spans a redshift range from 3.6 to 5.03. Our
photometry reflects the rest-frame
  SED longward of Ly alpha for all redshifts. The results show that the near-IR
colors of high redshift quasars are quite uniform. We have modelled the
continuum shape of the quasars (from just beyond Ly alpha to ~4000 A) with a
power law of the form f_nu \propto nu^alpha, and find <alpha > =-0.57 with a
scatter of 0.33. This value is similar to what is found for lower redshift
quasars over the same restframe wavelength range, and we conclude that there is
hardly any evolution in the continuum properties of optically selected quasars
up to redshift 5. The spectral indices found by combining near-IR with optical
photometry are in general consistent but slightly flatter than what is found
for the same quasars using the optical spectra and photometry alone, showing
that the continuum region used to determine the spectral indices can somewhat
influence the results.
