The γ-radiation-initiated polymerization of acrylonitrile (AN) at 25[ddot] C has been studied, both in aqueous solution and in emulsion, at dose rates between 70 and 175 krad/hr. The effect of added emulsifier, sodium lauryl sulfate (SLS), on reaction rates, Rp, and on polymer molecular weight, Mn, has been investigated. G (monomer polymerized) values ranged from 7,500 in aqueous solution to 20,000 in bulk to 45,000 in emulsion, all based on the total energy absorbed. In the aqueous solution polymerization, where Rpis approximately first order in initial monomer concentration over the range 0.15 ± [AN]o± 1.06 moles/liter, addition of SLS increases Rpbut does not influence the order of the reaction with respect to [AN]o. In the emulsion system at 70 krad/hr and at a phase volume ratio AN/H2O of 1/2, (PR = 1/2), Rpvaries as [SLS]0.1over the concentration range 0.01 ± [SLS] ± 2.5± wt/vol of aqueous phase. At the same PR value, and at 80 krad/hr, Mnof the polymer (measured by viscometry in dimethylformamide solution) is effectively independent of [SLS] in the range of 0.01 ± [SLS] ± 10± wt/vol of aqueous phase. Initial Rpvalues are either independent of PR in the range 1/3 ± PR ± 1/1 or exhibit an insensitive and unsystematic dependence thereon. Based on measurements at 70 and at 175 krad/hr, the intensity exponent of Rpat PR = 1/2 is approximately 0.4.