  The Ryle Telescope has been used to provide images at 15 GHz of the
Sunyaev-Zel'dovich decrements towards a dozen clusters in an X-ray
luminosity-limited sample. So far, X-ray data have allowed H_0 estimates
towards two of these, both giving ``low'' values that are self-consistent,
though it is essential to obtain many more estimates to reduce the effects of
cluster projection. We have also discovered a decrement towards the z=3.8
quasar pair PC1643+4631A&B (198'' separation); substantial X-ray, optical and
infrared follow-up show that the cluster responsible is either at z>1 or very
underluminous and that very significant gravitational lensing must be occuring.
