An analytical study is presented for the thermophoretic motion of two freely suspended aerosol spheres using a method of reflections. The particles are oriented arbitrarily with respect to the prescribed constant temperature gradient, and they are allowed to differ in radius, in thermal conductivity and in surface properties. The Knudsen numbers are assumed to be small so that the fluid flow is described by a continuum model with a thermal creep and a hydrodynamic slip at the particle surfaces. The method of reflections is based on an analysis of the thermal and hydrodynamic disturbances produced by a single sphere placed in an arbitrarily varying temperature field. The results for two-sphere interactions are correct to O(r(12)(-7)) where r(12) is the distance between the particle centers. For the special case of spheres oriented along the undisturbed temperature gradient, our results are in perfect agreement with the numerical solution obtained using bipolar coordinates. Based on a microscopic model the results for two-sphere interactions are used to find the effect of the volume fraction of particles of each type on the average thermophoretic velocity in a bounded suspension. For a suspension of identical spheres, this average velocity is reduced as the particle concentration is increased. In general, the effect of particle interactions on thermophoresis is much weaker than that on sedimentation.