A new method has been developed to measure the thermal diffusivity parallel to the surface of a platelike specimen using laser pulse heating. A pulsed laser beam which has a circular cross section is irradiated onto the front surface of the specimen. The time dependence of the temperature response of a circular area on the back surface at a certain distance from the irradiated area is determined using a radiation detector for which the spatial distribution of sensitivity is experimentally determined. The geometry of the apparatus is determined using standard specimens the thermal diffusivity of which is known. For isotropic samples, the values parallel to the surface obtained by the present method agree within 10% with those perpendicular to the surface obtained by the conventional pulse heating method. ©1996 American Institute of Physics.