  We present Sunyaev-Zel'dovich Effect (SZE) imaging observations of three
distant (z > 0.8) and highly X-ray luminous clusters of galaxies, Cl1226+33,
Cl0152-13 and MS1054-03. Two of the clusters, Cl1226+33 and Cl0152-13, were
recently discovered in deep ROSAT x-ray images. Their high X-ray luminosity
suggests that they are massive systems which, if confirmed, would provide
strong constraints on the cosmological parameters of structure formation
models. Our Sunyaev-Zel'dovich Effect data provide confirmation that they are
massive clusters similar to the well studied cluster MS1054-03. Assuming the
clusters have the same gas mass fraction as that derived from SZE measurements
of eighteen known massive clusters, we are able to infer their mass and
electron temperature from the SZE data. The derived electron temperatures are
9.8, 8.7, and 10.4 keV, respectively, and we infer total masses of ~2 x 10^14
h^-1 Msun within a radius of 65 arcsec (340 h^{-1} kpc) for all three clusters.
For Cl0152-13 and MS1054-03 we find good agreement between our SZE derived
temperatures and those inferred from X-ray spectroscopy. No X-ray derived
temperatures are available for Cl1226+33, and thus the SZE data provide the
first confirmation that it is indeed a massive system. The demonstrated ability
to determine cluster temperatures and masses from SZE observations without
access to X-ray data illustrates the power of using deep SZE surveys to probe
the distant universe.
