  We present results of a weak gravitational lensing survey of six X-ray
selected high-redshift clusters of galaxies. We find that the masses of the
clusters derived from weak lensing are comparable to those derived from the
X-ray observations. We show that many of the clusters have significant
substructure not observed in the X-ray observations and that for the more
massive clusters a singular isothermal sphere does not provide a good fit to
the radial mass profile.
