The radiolytic formation of molecular hydrogen has been studied in solutions of methyl bromide, sulfuric acid and iodine in N-methylpyrrolidin-2-one (NMP) and also in acidic aqueous solution of NMP using gas chromatography and vacuum techniques. The yield of H₂ in NMP was measured to be G(H₂)= 107 ± 7 nmol J^–1, which is rather low relative to other organic solvents. 61.6% of the H₂ formed comes from molecular processes and 38.4% from H˙ abstraction from NMP. The low yield is attributed to the fact that the natural decay of e^–_s does not lead to the formation of H₂. Experiments in acidic aqueous solution show that H-atom abstraction from NMP by H^·, rather than addition to the carbonyl group, is the kinetically favoured reaction. The rate constant for the abstraction is 2.1 × 10⁷ dm³ mol^–1 s^–1, which is estimated to be ca. 200 times faster than the addition reaction. A reaction scheme is proposed for the behaviour of e^–_s and the formation of H₂.