Portland cement stone samples simulating solidified active waste were 60Co-gamma-irradiated with doses up to 108 rad. The radiolytically produced gases were determined using a gas chromatographic technique. Various additives chemically comparable to actual low- and intermediate-level wastes were incorporated in the cement mixtures. Also the influence of the presence of oxygen during the irradiation was investigated. In no case could or NOx (from the decomposition of nitrate) be detected. In nitrate-free samples, only H2 is produced. The H2 yield ranges between 3 and 8 ml of H2 per kilogram of cement stone and per megarad radiation applied. It depends on the water content and the aging time of the samples; an influence of the concrete fluidizer content was not observed. The presence of nitrate in the samples gives rise to the production of O2 besides H2 and an overall decrease of the gas yield.