The study described in this article was conducted in 1966 to determine the fumigant potential of GC-10033 (tetrachlorocyclopropene) against stored-product insects in space and in the grain mass. Test insects were: Confused flour beetle adults, cigarette beetles (Lasioderma serricorne), and, black carpet beetle larvae. GC-10033 was more toxic to the test insects than was methyl bromide. Further studies were to be conducted.