  We show that the high local baryonic fraction, M(bar) ~ 1/3 M(tot), found in
groups and clusters of galaxies does not reconcile the observed cosmological
baryon density with the standard Big-Bang prediction. Taking into account
recent measurements on the hot-gas content and temperature functions of
clusters and groups, we get Omega(gas) = 0.0023 h_{50}^{-1.5} ~ 4% Omega(BBN).
Including the contributions of galaxies and of (local) Ly-alpha clouds we
estimate Omega(bar) ~ 0.004-0.006 < 10% Omega(BBN) as the amount of detected
baryons. Most of the synthesised atoms are still to be discovered. We propose
to relate the impressive presence of the hot gas component in clusters with the
very low, mass-dependent efficiency of the process of galaxy formation in
making stars from the primordial gas.
