  Annual modulation due to the Earth's motion around the Sun is a well known
signature of the expected WIMP signal induced in a solid state underground
detector. In the present letter we discuss the prospects of this technique on
statistical grounds, introducing annual-modulation sensitivity plots for the
WIMP-nucleon scalar cross section for different materials and experimental
conditions. The highest sensitivity to modulation is found in the WIMP mass
interval 10 GeV< m_W < 130 GeV, the actual upper limit depending from the
choice of the astrophysical parameters, while the lowest values of the
explorable WIMP-nucleon elastic cross-sections fall in most cases within one
order of magnitude of the sensitivities of present direct detection WIMP
searches.
