Purity >97% by HPLC. N-methyl-4-hydrazino-7-nitrobenzofurezan (MNBDH) is a new reagent for the determination of aldehydes and ketones. MNBDH reacts with carbonyl copmounds in acidic media to the corresponding MNBD-hydrazones. For example formaldehyde hydrazone formed is determined by high-performance liquid chromatography with UV/visible detection at 474 nm. MNBDH has been studied recently as a reagent with reduced interferences by ozone and nitrogen dioxide. It reacts with these oxidants to give only one product N-methyl-4-amino-7-nitrobenzofurezan (MNBDA).