  Corrections to the magnitudes of high redshift objects due to intergalactic
attenuation are computed using current estimates of the properties of the
intergalactic medium. The results of numerical simulations are used to estimate
the contributions to resonant scattering from the higher order Lyman
transitions. Differences of 0.5-1 magnitude from the previous estimate of Madau
(1995) are found. Intergalactic k_IGM-corrections and colours are provided for
high redshift starburst galaxies and Type I and Type II QSOs for several filter
systems used in current and planned deep optical and infra-red surveys.
