The three‐dimensional equation of heat conduction is solved to obtain the time‐dependent (harmonic) temperature field in an opaque, thermally anisotropic layer on a thermally thick and isotropic substrate when the system is heated by a modulated Gaussian laser beam. The influence of the anisotropy on the amplitude and phase response of the temperature variation as a function of the position on the surface and depth in the layer is studied. The limiting case of one‐dimensional heat diffusion in highly anisotropic media is discussed. For one example the influence of thermal anisotropy on the frequency dependence of the surface temperature distribution is studied. ©1995 American Institute of Physics.