The sensitivity of THERA to different models of ``new physics'' has been studied, both for the contact interaction approximation and for the resonance production. For contact interaction models conserving parity, scales up to about 18 TeV can be explored at THERA, extending considerably beyond the existing bounds. Significant improvement of existing limits is also expected for models with large extra dimensions. Effective Plank mass scales up to about  2.8 TeV can be probed. THERA will be the best machine to study leptoquark properties, for leptoquark masses up to about 1 TeV. It will be sensitive to the leptoquark Yukawa couplings down to \lambda _LQ \sim 10^-2.

PACS numbers: 12.60.Rc, 12.60.i, 13.60.Hb, 14.80.j