  We analyze the possibility that neutrino telescopes may provide an
experimental determination of the slope lambda of the gluon distribution in the
proton at momentum fractions x smaller than the accelerator reach. The method
is based on a linear relation between lambda and the spectral index (slope) of
the down-going atmospheric muon flux above 100 TeV, for which there is no
background. Considering the uncertainties in the charm production cross section
and in the cosmic ray composition, we estimate the error on the measurement of
lambda through this method, excluding the experimental error of the telescopes,
to be ~ +/- 0.2
