The e.p.r. spectra of polycrystalline RDX, and its single crystals, when irradiated with γ-radiation and 254 nm light at 77–298 K, indicate that ˙NO2 may be a primary photochemical product of RDX. Mass spectral analyses of the gaseous products suggested that N2 and NO may also be primary photolysis products of RDX. The identity of these products was consistent with the theoretically predicted bond cleavage patterns of the axial and equatorial nitramine groups of RDX and HMX. A combination of theory and experiment thus permitted the tentative assignment of the primary photochemical steps for polycrystalline RDX.