The measurements of hadron and lepton-pair production cross sections and lepton-pair forward–backward asymmetries performed with the L3 detector at centre-of-mass energies between 130 GeV and 172 GeV are used to search for new physics phenomena. New physics effects involving four fermion vertices – contact interactions – are looked for in all channels. For hadron production the exchange of virtual leptoquarks and scalar quarks is studied. No evidence for deviations from the Standard Model expectations is found. Lower limits on the scale Λ of contact interactions in the range 1.2–7.1 TeV are obtained at the 95% confidence level for various models. Upper limits on the coupling strengths of leptoquarks and scalar quarks are derived.Facultad de Ciencias Exactas