A new technique for the direct determination of radiolytically produced gaseous products is discussed. The method consists of continuously bubbling a gas through a sample cell and monitoring the effluent with a mass spectrometer. It has been applied to the determination of H/sub 2/ and CO/sub 2/ produced in various aqueous solutions irradiated with /sup 60/Co ..gamma.. radiation. The yield of H/sub 2/ is found to be 0.51 molecules/100 eV in aerated ferrous sulfate solutions and in deaerated KBr solutions. The effect of saturating the ferrous sulfate solution with oxygen or addition of KNO/sub 2/ to the KBr solution is the same with a yield of H/sub 2/ of 0.43 molecules/100 eV. The yield of OH radicals as determined by the production of CO/sub 2/ in dilute oxygen-saturated formic acid solutions is 2.5 molecules/100 eV.