  The search for rare particles in the cosmic radiation remains one of the main
aims of non-accelerator particle astrophysics. Experiments at high altitude
allow lower mass thresholds with respect to detectors at sea level or
underground. The SLIM experiment is a large array of nuclear track detectors
located at the Chacaltaya High Altitude Laboratory (5290 m a.s.l.). The
preliminary results from the analysis of a part of the first 236 sq.m exposed
for more than 3.6 y are here reported. The detector is sensitive to
Intermediate Mass Magnetic Monopoles and to SQM nuggets and Q-balls, which are
possible Dark Matter candidates.
