  We use data on the deep inelastic structure function F_2 in order to
constrain the cross-section for scattering a colour dipole off a proton. The
data seem to prefer parameterisations which include saturation effects. That is
they indicate that the strong rise with energy of the dipole cross-section,
which holds for small dipoles, pertains only for r < r_s(x) where r_s(x)
decreases monotonically as x decreases. Subsequent predicitions for the
diffractive structure function F_2^{D(3)} also hint at saturation, although the
data are not really sufficiently accurate.
