  Recently, models proposing superheavy particles $X$ as source of ultrahigh
energy cosmic rays have attracted some interest. The $X$-particles are either
metastable relic particles from the early Universe or are released by
topological defects. In these models, the detected air-showers are produced by
primaries originating from the fragmentation of the $X$-particles. We present
the fragmentation spectrum of superheavy particles calculated in SUSY-QCD. Then
we discuss the status of the lightest supersymmetric particle as possible
ultrahigh energy primary.
