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 eq. The second part is devoted to contact terms. The bounds on the mass scale A 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.This work was partially supported by CICYT under contract AEN96-1672 and by Junta de Andalucía
