Eyre and Smithies have recently obtained radical yields of [Formula: see text] in the radiolysis of gaseous ammonia. The consistency of these with N2, H2, and N2H4 yields obtained in the high dose rate radiolysis of NH3 and NH3–C3H6 mixtures has been shown by numerical integration of the rate expressions in a simple radical mechanism. These calculations give a value of 2.1 ± 0.5 × 1010 M−1 s−1 for the reaction of H atoms and NH2 radicals and a ratio of recombination to disproportionation of 6:1.