  We investigate the effects on cosmological density perturbations of dark
radiation in a Randall-Sundrum 2 type brane-world. Dark radiation in the
background is limited by observational constraints to be a small fraction of
the radiation energy density, but it has an interesting qualitative effect in
the radiation era. On large scales, it serves to slightly suppress the
radiation density perturbations at late times, while boosting the perturbations
in dark radiation. In a kinetic (stiff) era, the suppression is much stronger,
and drives the density perturbations to zero.
