  In recent years, upper limits on the cosmic microwave background (CMB)
anisotropies combined with predictions made by theories of galaxy formation,
have been extremely powerful in ruling out purely baryonic dark matter (BDM)
universes. However, it has recently been argued that the absence of a prominent
second peak in the anisotropy spectrum measured by the BOOMERanG-98 and
MAXIMA-1 experiments seems to favour a $\Lambda$BDM model when combined with
standard Big Bang Nucleosynthesis (BBN) constraints. In this {\it Letter}, we
further investigate this result showing that, using the CMB data {\it alone}, a
purely baryonic adiabatic model of structure formation seems unlikely if the
universe is flat ($\Omega=1$). Combining the CMB data with supernova type Ia
(SNIa) data renders purely baryonic models inconsistent with flatness at high
significance and more than $3 \sigma$ away from both the BBN constraints and
the HST key project result $h=0.72 \pm 0.08$. These results indicate that only
a radical revision of cosmology with {\it ad hoc} properties could bring
baryonic models such as those advocated by MOND enthusiasts back into agreement
with current observations.
