  It is shown that the observation of the spectra of leading neutrons from
proton beams can be a good probe of absorptive and migration effects. We
quantify how these effects modify the Reggeized pion-exchange description of
the measurements of leading neutrons at HERA. We are able to obtain a
satisfactory description of all the features of these data. We also briefly
discuss the corresponding data for leading baryons produced in hadron-hadron
collisions.
