A chemical derivatization scheme has been developed for the sensitive and selective determination of hydrazine, monomethylhydrazine (MMH) and 1,1-dimethylhydrazine (UDMH) by fluorescence spectrometry. Incorporation of hydrazine into an aromatic framework by derivatization with o-phthalaldehyde (OPA), naphthalene-2,3-dicarbaldehyde (NDA), or anthracene-2,3-dicarbaldehyde (ADA) creates an efficient fluorophore the emission wavelength of which is red-shifted from the original reagent. The fluorescence emission for each of the different derivatizing reagents (OPA, NDA, and ADA), is minimal and nearly within the noise of the background. The hydrazine derivatives, on the other hand, are intensely fluorescent and characterized by a broad fluorescence emission centred at 376 nm for OPA, 500 nm for NDA, and 549 nm for ADA. For the NDA hydrazine derivative, a linear concentration dependence is observed from 50 ng l^–1 to 500 µg l^–1 of hydrazine (correlation coefficient, r > 0.999). The response time necessary to give 90% of a full-scale response is <2 min. The response of the ADA reagent is similar; however, its response time is faster (<0.5 min), and its detection limit is higher (150 ng l^–1). By careful control of the pH and the aromatic dicarbaldehyde chosen, it is possible to differentiate quantitatively between the hydrazine, MMH, and UDMH levels present in mixed samples. The detection limits for MMH and UDMH using the NDA reagent are 120 ng l^–1 and 40 µg l^–1, respectively.