The reactions of 1,1-dimethylhydrazine with 2,3,5-triphenyl-2Н-tetrazolium and 2,5-diphenyl-3-(4-nitrophenyl)-2Н-tetrazolium chlorides in a solution and on a cellulose carrier have been studied by means of spectrophotometry and chromato–mass spectrometry to develop new chromogenic indicators for detection of 1,1-dimethylhydrazine. 1,3,5-Triphenylformazan and 1,3-diphenyl-5-(4-nitrophenyl)formazan are formed in these reactions, respectively; deep red shifts have been observed. Other products of these reactions result from oligomerization and addition of short-living 1,1-dimethylhydrazyl and tetrazolium radicals.