A beam source of atomic hydrogen is described which produces metastable atoms in the 2S1/2state by optical pumping. A beam flux of 1016atoms/s is generated in the ground state. The atoms in the beam pass in front of a lamp producing Lyman‐&bgr; (1026 A˚) radiation, where some of them are excited to the 3Plevel and cascade with a branching ratio of 12% to the 2S1/2state. The number of metastable atoms produced is measured by quenching them with an electric field and detecting the emitted Lyman‐&agr; (1216 A˚) radiation. Beams of 106metastable atoms/s were obtained. Using the Bethe‐Lamb theory for the quenching process, a metastable beam effective temperature of 100 K was measured.