Probabilities of excitation by electron impact on the 21S and 23S metastable levels of atomic helium, to a large number of higher levels in the n1S, n1P, n1D, n3S, n3P and n3D series, are measured, with the objective of understanding the basic physics of collisional interactions with metastable atoms. Cross sections for ionization out of the 21S and 23S metastable levels are also measured.
