  We show how future measurements of the SZ effect (SZE) can be used to
constrain the cosmological parameters. We combine the SZ information expected
from the Planck full-sky survey, N(S), where no redshift information is
included, with the N(z) obtained from an optically-identified SZ-selected
survey covering less than 1% of the sky. We demonstrate how with a small
subsample (approx. 300 clusters) of the whole SZ catalogue observed optically
it is possible to drastically reduce the degeneracy among the cosmological
parameters. We have studied the requirements for performing the optical
follow-up and we show the feasibility of such a project. Finally we have
compared the cluster expectations for Planck with those expected for Newton-XMM
during their lifetimes. It is shown that, due to its larger sky coverage,
Planck will detect a factor approx. 5 times more clusters than Newton-XMM and
also with a larger redshift coverage.
