Data on thermal radio emission and absorption in and near the directions towards supernova remnants are used to estimate the distribution of ionized gas surrounding remnants of type II supernovae. The amount of absorption and emission toward the supernova remnants are determined by two types of HII regions. The first are extended HII regions around the supernova remnants (Stromgren spheres), while the second are more compact and bright HII regions surrounding early-type stars. In the early stages of evolution of the supernova remnants (1000–3000 yrs), the amount of thermal absorption and emission is minimum, apparently indicating that only the supernova Stromgren zones contribute in these stages, while there is an absence of absorption or emission from the compact HII regions. Possible mechanisms for this scenario are discussed.