We have applied two photothermal techniques (infrared radiometry and mirage) and conventional procedures to measure the thermal diffusivity of a highly anisotropic sample of pyrolytic graphite. Unexpected and strongly differing results are obtained with each technique. A theoretical analysis indicates that whereas the mirage technique gives a measure of the elements of the thermal diffusivity tensor, infrared radiometry yields the elements of another thermal magnitude represented by the inverse of this tensor. ©1995 American Institute of Physics.