We report on anisotropic wave mixing in planar iron-doped titanium-indiffused LiTaO₃ waveguides. The diffusion of titanium in Y-cut LiTaO₃ is investigated for different temperatures and diffusion times, yielding the diffusion constant. Material properties of the waveguides such as conductivity and nondiagonal photovoltaic tensor elements are investigated by two-wave mixing of orthogonally polarized modes. Phase conjugation in waveguides by anisotropic four-wave mixing is demonstrated, too, and experimental results are compared with numerical solutions of the corresponding system of coupled-wave equations. © 1994 Optical Society of America.