  We report the results of new Hubble Space Telescope imaging of the positions
of six ultraluminous X-ray sources (ULXs). Using images in three ACS filters we
detect good candidate counterparts to four out of six ULXs, with one more
possible detection, and observed magnitudes in the range m ~ 22 - 26 in the
F606W filter. The extinction-corrected colours and absolute magnitudes vary
from source to source, even after correcting for additional extinction in the
host galaxy, and only one counterpart is readily explained as an OB star.
Nevertheless, these counterparts are decent candidates for future follow-up in
pursuit of dynamical mass constraints on the likely black holes powering these
sources.
