The theory of stimulated thermal scattering of trains of short light pulses is developed. Peculiar new effects are predicted for forward scattering, especially a critical dependence on the angle between scattered light and pump light. Particular emphasis is directed to the problem of pure thermal scattering. The dominant contribution to the stimulated scattering is in general due to density variations, no matter how short the light pulses are. Only under specific conditions is the density variation eliminated, allowing the observation of the pure thermal effect. © 1969 The American Physical Society.