  We discuss the problem of ultra high energy particles propagation in
astrophysical backgrounds. We present two different computational schemes based
on both kinetic and Monte Carlo approaches. The kinetic approach is an
analytical computation scheme based on the hypothesis of continuos energy
losses while the Monte Carlo scheme takes into account also the stochastic
nature of particle interactions. These schemes, that give quite reliable
results, enable the computation of fluxes keeping track of the different
primary and secondary components, providing a fast and useful workbench to
study Ultra High Energy Cosmic Rays.
