  We report the results of a programme of dual-epoch Chandra ACIS-S
observations of five ultraluminous X-ray sources (ULXs) in nearby spiral
galaxies. All five ULXs are detected as unresolved, point-like X-ray sources by
Chandra, though two have faded below the 10^39 erg/s luminosity threshold used
to first designate these sources as ULXs. Using this same criterion, we detect
three further ULXs within the imaged regions of the galaxies. The ULXs appear
to be related to the star forming regions of the galaxies, indicating that even
in ``normal'' spiral galaxies the ULX population is predominantly associated
with young stellar populations. A detailed study of the Chandra ACIS-S spectra
of six of the ULXs shows that five are better described by a powerlaw continuum
than a multi-colour disc blackbody model, though there is evidence for
additional very soft components to two of the powerlaw continua. The measured
photon indices in four out of five cases are consistent with the low/hard state
in black hole binaries, contrary to the suggestion that powerlaw-dominated
spectra of ULXs originate in the very high state. A simple interpretation of
this is that we are observing accretion onto intermediate-mass black holes,
though we might also be observing a spectral state unique to very high mass
accretion rates in stellar-mass black hole systems. Short-term flux variability
is only detected in one of two epochs for two of the ULXs, with the lack of
this characteristic arguing that the X-ray emission of this sample of ULXs is
not dominated by relativistically-beamed jets. The observational
characteristics of this small sample suggest that ULXs are a distinctly
heterogeneous source class.
