  The possible contributions of the various classes of extragalactic sources
(including, in addition to the canonical radio sources, GHz Peaked Spectrum
sources, advection-dominated sources, starburst galaxies, high-redshift
proto-spheroidal galaxies) to the arcminute scale fluctuations measured by the
CBI, BIMA, and ACBAR experiments are discussed. At 30 GHz, fluctuations due to
radio sources undetected by ancillary low-frequency surveys may be higher than
estimated by the CBI and BIMA groups. High-redshift dusty galaxies, whose
fluctuations may be strongly enhanced by the effect of clustering, could
contribute to the BIMA excess signal, and dominate at 150 GHz (the ACBAR
frequency). Moreover, in the present data situation, the dust emission of these
high-redshift sources set an unavoidable limit to the detection of primordial
CMB anisotropies at high multipoles, even at frequencies as low as $\simeq 30$
GHz. It is concluded that the possibility that the excess power at high
multipoles is dominated by unsubtracted extragalactic sources cannot be ruled
out. On the other hand, there is room for a contribution from the
Sunyaev-Zeldovich effect within clusters of galaxies, with a density
fluctuation amplitude parameter $\sigma_8$ consistent with the values preferred
by current data.
