Two fluorometric methods for analysis of hydrochlorothiazide (HCT) are described utilizing direct measurement of thin-layer plates. The first method employs a modification of the Bratton-Marshall reaction and is therefore applicable to all aromatic primary amines. Following diazotation and azocoupling of the HCT hydrolysis product, a fluorescent group is added to the compound. For this purpose N-(1-naphthyl)ethylenediamine is first coupled with 4-chloro-7-nitrobenzo-2,1,3-oxadiazole. In the second method, the intrinsic fluorescence of underivatized HCT, following its extraction from plasma, urine or saliva, is used. It is shown that the sensitivity of this method is sufficient for estimating the kinetics following oral administration of 25 mg HCT.