  Applications of perturbative QCD to hard exclusive electroproduction
processes in the Bjorken limit at small invariant momentum transfer t bring in
a new type of parton distributions which have hybrid properties, resembling
both the parton distribution functions and the distribution amplitudes. Their
t-dependence is analogous to that of hadronic form factors. We discuss general
properties of these new parton distributions, their relation to usual parton
densities and the evolution equations which they satisfy.
