  I develop a phenomenological approach to the description of the noise levels
that the space-time foam of quantum gravity could induce in modern gravity-wave
detectors. Various possibilities are considered, including white noise and
random-walk noise. In particular, I find that the sensitivity level expected
for the planned LIGO and VIRGO interferometers and for the next upgrade of the
NAUTILUS resonant-bar detector corresponds to a white-noise level which can be
naturally associated with the Planck length.
