Vaporized hydrogen peroxide (VHP) has proven efficacy for biological decontamination and is a common gaseous sterilant widely used by industry. Regarding chemical warfare agent decontamination, VHP is also effective against HD and VX, but not GD. Simple addition of ammonia gas to VHP affords reactivity toward GD, while maintaining efficacy for HD (and bioagents) and further enhancing efficacy for VX. Thus, modified VHP is a broad-spectrum CB decontaminant suitable for fumigant-type decontamination scenarios, i.e., building, aircraft, and vehicle interiors and sensitive equipment. Finally, as an interesting aside to the current study, commercial ammonia-containing cleaners are also shown to be effective surface decontaminants for GD, but not for VX or HD.