  We study the collisional energy loss suffered by an energetic parton
travelling the distance L in a high temperature quark-gluon plasma and
initially produced in the medium. We find that the medium-induced collisional
loss -Delta E(L) is strongly suppressed compared to previous estimates which
assumed the collisional energy loss rate -dE/dx to be constant. The large L
linear asymptotic behaviour of -Delta E(L) sets in only after a quite large
retardation time. The suppression of -Delta E(L) is partly due to the fact that
gluon bremsstrahlung arising from the initial acceleration of the energetic
parton is reduced in the medium compared to vacuum. The latter radiation
spectrum is sensitive to the plasmon modes of the quark-gluon plasma and has a
rich angular structure.
