Abstract. The collisions Be--He and Mg ~-He have been studied from 10 to 75 keV by means of optical spectrometry. Relative excitation cross sections and polarizations have been measured at 40 keV for S through G terms with principal quantum number n up to 10. Within a Rydberg series the excitation cross sections are found to decrease monotonically with n, and the excited terms have in general a negative alignment.