Sidescatter of CO2laser light from underdense, laser‐heated plasmas in H2and He is observed at &Vthgr;=90°. Spectrum, exponentiation, isotropy, and polarization measurements are used to deconvolve two separate mechanisms: (1) Doppler‐shifted reflections from moving dielectric discontinuities created in the laser‐ionization process, and (2) Stimulated Brillouin scattering seeded by these reflections. The dielectric sidescatter is unpolarized and azimuthally symmetric, similar to the diffuse component of scattering in solid‐target experiments. The Brillouin sidescatter saturates at a low level corresponding to an ion wave amplitude of 0.1–1.0%, consistent with previous data on the saturation of backscatter.