Abstract The profile of the hydrogen Hβ line emitted by a hydrogen low-temperature afterglow plasma has been measured at electron densities 1.8·1015 , 1·1015 and 5·1014 cm-3 by means of a 10-channel analyzer system with a spectral resolution of 0.1 Å. All profiles showed weak plasma satellites suddenly appearing at wavelength distances which correspond to the electron plasma frequency and showing “satellite line wings” which slowly smooth out at larger wavelength distances. In the line core-where all quasi-static and ion dynamic theories predict a minimum - appeared an intensity maximum well separated from the closely spaced intensity shoulders. This new feature not yet predicted by line broadening theories and not yet observed by other experimentalists is probably due to low-frequency ion oscillations which couple with the excited atomic system. Such an effect would explain discrepancies between available Stark broadening theories and the mass-dependent structure of line profiles recently observed in other experiments. The effect may possibly be useful for measuring collective low-frequency oscillations in plasmas under very special conditions.