The radio continuum emission of long-period variables (LPVs) in the continuum is considered. For some LPVs (e.g., R Aql and V Hya) weak emission, observed at centimeter wavelengths, can be explained by thermal free-free radiation of the ionized gas behind the shock front in the stellar atmosphere. The ionized layer behind the shock remains optically thick at the wavelengths as short as 1 cm; the brightness temperature found for R Aql at 2 cm by Drake et al. (1987, AJ, 94, 1280), Tb = 18000 K, is consistent with the expected temperature behind the shock.