This talk is divided in two parts. In the first one we discuss the signals of
the Minimal Supersymmetric Standard Model through the production of \tilde{e}
\tilde{q}. The second part is devoted to contact terms. The bounds on the mass
scale Lambda obtained from atomic parity violation experiments and from LEP are
reviewed. Afterwards, we show that the excess of events at high Q^2 observed at
HERA could be explained in terms of these contact terms.Comment: 15 pages. LaTeX2e, 3 Postscript figures included. Talk presented by
F. Cornet at the XXI International School on Theoretical Physics, Ustron
(Poland), September 1997. To appear in Acta Physica Polonica
