(2-Bromo-2-hydroxyiminoacetyl)furazans and -furoxans were synthesized by nitrosation of bromoacetylfurazans and -furoxans with nitrosylsulfuric acid in conc. H2SO4 An efficient method for preparing the previously unknown 3,4-bis[furazanoyl(or furoxanoyl)]furoxans has been proposed; it consists of the reaction of acetylfurazans and acetylfuroxans with a mixture of a nitrating reagent and a catalytic amount of a nitrosating reagent in conc. H2SO4.