  The CMB anisotropy on arc second range is examined to test the power spectrum
of perturbations in the small scale region and, in particular, to estimate the
mass of dominant dark matter particles. It is shown that for the simplest
evolutionary history with standard recombination, three and four beam
observations could discriminate the mass of dark matter particles in the
interval $0.5 KeV\leq M_{DM}\leq 4 KeV$ with an antenna beam (0.5 - 0.25) arc
minute with amplitude $\approx 10^{-7}$.
