The effect of a temperature-dependent surface tension upon the instability of film flow down a heated inclined plane is investigated for long-wavelength disturbances. For 2-D waves, a quadratic equation for the critical Reynolds number results. One root of this equation corresponds to a hydrodynamic instability as modified by thermocapillary action, whereas the other root corresponds to a thermocapillary instability as modified by shear. As the Marangoni number increases, the roots approach each other and eventually become equal. Thereafter, the flow is unstable for all Reynolds numbers. 2-D waves are found to be more unstable than longitudinal rolls. The numerical results are presented in a form appropriate to an experiment in which the Reynolds number varies by changing the film thickness or the angle of inclination.