Ultrahigh energy cosmic rays and supersymmetry

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.