Beams of metastable helium produced by electron bombardment generally contain atoms in both the 21Sand 23Sstates. It is important in many experiments to distinguish between these states, or at least to know the population ratio. A beam of 23Sand ground state helium atoms has been produced by electron bombardment and subsequent resonant quenching of 21Satoms with 21S−21P2 &mgr; radiation. This radiation mixes the 21Sand 21Pstates, the latter decaying primarily to the 11Sstate by emission of 584 Å radiation. The quenching has been studied as a function of beam atom velocity. The results indicate that beams of metastable helium containing less than 1% 21Satoms can be produced.