  We report high spatial resolution HST imagery and photometry of three
well-studied, intense galactic X-ray binaries, X2129+47, CAL 87 and GX17+2. All
three sources exhibit important anomalies, not readily interpreted by
conventional models. Each source also lies in a severely crowded field, and in
all cases the anomalies would be removed if much of the light observed from the
ground in fact came from a nearby, thus-far-unresolved superposed companion.
For V1727 Cyg (X2129+470), we find no such companion. We also present an HST
FOS spectrum and broadband photometry which is consistent with a single, normal
star. The supersoft LMC X-ray source CAL 87 was already known from ground-based
work to have a companion separated by 0.9'' from the optical counterpart; our
HST images clearly resolve these objects, and yield the discovery of an even
closer, somewhat fainter additional companion. Our photometry indicates that
contamination is not severe outside eclipse, where the companions only
contribute 20% of the light in V, but during eclipse more than half of the V
light comes from the companions. The previously-determined spectral type of the
CAL 87 secondary may need to be reevaluated due to this significant
contamination, with consequences on inferences of the mass of the components.
We find no companions to NP Ser (=X1813-14, =GX17+2). However, for this object
we point out a small but possibly significant astrometric discrepancy between
the position of the optical object and that of the radio source which is the
basis for the identification. This discrepancy needs to be clarified.
