Type-304 stainless steel (SS), irradiated to a range of fast (E > 1 MeV) neutron fluences (1.90 × 10¹⁸ to 9 × 10²¹ n/cm²) in several different boiling water reactors, was found to contain ≥3 times as much hydrogen as unirradiated material. Hydrogen buildup in irradiated Type-304 SS was independent of fluence and flux in the range of fluences and fluxes investigated. This study was conducted as part of an investigation of irradiation-assisted stress corrosion cracking (IASCC). The accumulation of hydrogen in irradiated Type-304 SS may exacerbate the irradiation-induced loss of ductility, thereby increasing susceptibility to IASCC, or it may contribute to IASCC by other means.