  The CMB is already one of the pillars of the Big Bang model. However it may
also become our most powerful tool to distinguish contending models and to
determine their cosmological parameters. To realize this goal, more than 20
observational groups and two new satellites are gearing up to make precise
measurements of the CMB at small angular scales. In such a situation it is
important to keep track of what the CMB data can already say about cosmological
parameters. Current CMB data can already be used to constrain cosmological
parameters. The results are model dependent. We have obtained contraints on
Hubble's constant h and the density of the Universe Omega_{o} in the context of
open and critical density CDM models with Lambda=0. In critical density models
we obtain h=0.30^{+0.18}_{-0.07}. This low value is inconsistent with direct
measurements of h but fully consistent with four other cosmological
measurements: Big Bang nucleosynthesis, cluster baryonic fraction, age
constraints from globular clusters and limits on the shape parameter Gamma of
matter power spectra (in Omega_{o}=1 models). If Omega_{o} is left as a free
parameter the constraints on h are less restrictive: h=0.40^{+0.57}_{-0.14}.
This is fully consistent with local $h$ measurements and the four other
cosmological measurements mentioned above. The best-fit density is Omega_{o}=
0.85 and we set an upper limit of Omega_{o} > 0.4 at ~ 95% CL. At this
conference Ostriker has claimed that open-CDM models with Omega_{o} ~ 0.3 and h
~ 0.70 are compatible with all current data. However our new CMB data analysis
rules this model out at more than ~ 4 sigma.
