We have measured ac magnetoresistance in fields up to 8 T in a variety of YBa2Cu3O7−&dgr;single crystals containing (a) twin boundaries only in one direction, (b) multi‐twin domain structure, and (c) growth steps. We find two components of the resistance: an angulardependentLorentz force induced ‘‘excess resistivity’’ superimposed on an angularindependentresistivity. The temperature and magnetic field dependence of the angular‐dependent resistivity exhibit a strong correlation with crystal defects, whereas the angular‐independent resistivity remains virtually unchanged. In addition, we find crystals exhibiting both ohmic and non‐ohmic behavior in theirI‐Vcharacteristics depending on crystal imperfections.