A series of experiments was performed with selected reagents that were added to inhibit the reduction of Np(VI) to Np(V) during irradiation of its solutions in HNO3. Acetamide and methylurea as nitrous acid scavengers, and vanadium(V) as a neptunium(V) oxidizer, were examined in this effort. Solutions of these reagents in 4M HNO3 were irradiated in a Co-60 gamma irradiator. Additions of 1-10mM of methylurea and vanadium(V) essentially had no effect on the final oxidation state of Np after irradiation with a dose of 60kGy, while the addition of higher concentrations of methylurea (50 and 100mM) led to an almost complete reduction of Np to the tetravalent oxidation state.