  Compton scattering of the cosmic microwave background radiation by electrons
in the hot gas in clusters of galaxies - the Sunyaev-Zeldovich effect - has
long been recognized as a uniquely important feature, rich in cosmological and
astrophysical information. We briefly describe the effect, and emphasize the
need for detailed S-Z and X-ray measurements of nearby clusters in order to use
the effect as a precise cosmological probe. This is the goal of the MITO
project, whose first stage consisted of observations of the S-Z effect in the
Coma cluster. We report the results of these observations.
