For the sensitive detection of solutes in the picomole to nanogram range, fluorimetric analyses are often adopted. As there are growing needs for quantifying specifically and sensitively naturally occurring thiols and for measuring therapeutic concentrations of thiol-containing drugs, several fluorigenic reagents for thiols have been developed and some of them now are being used as pre- and post-column derivatization reagents in HPLC. HPLC combined with fluorescence detection is one of the most suitable techniques for the specific and sensitive determination of thiols because of its effective separation and selective detection. A few types of relevant reagents (dansylaziridine, maleimides, bimanes, and halogenobenzofurazans) were used for this purpose. All of them show promise for the analysis of various samples; likewise they each have their limitations. Dansylaziridine is fluorescent itself and gives an interfering peak in the chromatograms. The various substituted maleimides form multiple fluorescent products because of hydrolysis of the fluorophors. Bimanes produce several reagent peaks in the chromatograms and may react with non-thiolic functional groups, while several halogenobenzofurazans require drastic derivatizing conditions. The present work summarizes the current state of the art of thiol determinations using HPLC and fluorescence derivatization, with emphasis on the measurement of drugs in biological samples.