  We have investigated the rest-frame optical and far-infrared properties of a
sample of extremely bright candidate Lyman-break galaxies (LBG) identified in
the Sloan Digital Sky Survey. Their high ultraviolet luminosities and lack of
strong ultraviolet emission lines are suggestive of massive starbursts,
although it is possible that they are more typical luminosity LBGs which have
been highly magnified by strong gravitational lensing. Alternatively, they may
be an unusual class of weak-lined quasars. If the ultraviolet and submillimetre
properties of these objects mirror those of less luminous, starburst LBGs, then
they should have detectable rest-frame far-infrared emission. However, our
submm photometry fails to detect such emission, indicating that these systems
are not merely scaled-up (either intrinsically or as a result of lensing)
examples of typical LBGs. In addition we have searched for the morphological
signatures of strong lensing, using high-resolution, near-infrared imaging, but
we find none. Instead, near-infrared spectroscopy reveals that these systems
are, in fact, a rare class of broad absorption-line (BAL) quasars.
