Calculations were made to estimate the amount of helium generated by irradiating stainless steel in advanced fast and thermal reactors. The sources and rates of helium production were determined for AISI type-304 stainless steel, a prime material for fuel cladding and reactor structural components. Reactor spectra were incorporated into the study to obtain more representative reaction rates in the two different reactors. Lack of cross-section data limits the accuracy of these calculations. Uncertainties in the estimates are presented, and the implications of the results are discussed.