  After introducing the notion of BPS preons as the basic constituents of
M-theory, we discuss the recent negative results in the search for solutions of
the D=10 and D=11 supergravity equations preserving 31/32 supersymmetries i.e.,
of preonic solutions. The absence of these supergravity preonic solutions may
point out to a pure quantum nature of BPS preons, manifesting itself in the
need of incorporating quantum (stringy/M-theoretic) corrections to the
supergravity equations.
