The energy and force of interaction of an extended screw dislocation with spherical and tetragonal defects were calculated for several fcc metals using anisotropic and isotropic elasticity theories. It is shown that anisotropy has a large effect on the magnitude of interaction energy and interaction force, as well as on the shape of the energy‐distance and force‐distance curves. The maximum value of the interaction energy was always smaller in the anisotropic case than in the isotropic case. But the maximum resisting force to dislocation motion due to defect‐dislocation interaction is not always smaller in the anisotropic crystal. Computation of the hardening coefficient at 0 °K for several fcc metals indicates that tetragonal defects cause significantly larger hardening than spherical defects.