Abstract Substituted 2-aminothiophenols (7 species) were evaluated for fluorescence derivatization reagents of aromatic aldehydes in spectrofluorimetry and liquid chromatography. Of the compounds, 2-amino-5-methoxythiophenol was the most favourable in practical use. The reagent reacts selectively with aromatic aldehydes in acidic media within 70 min at 50°C. The fluorescent products from benzaldehyde and 4-hydroxybenzaldehyde are shown to be 2-phenyl-6-methoxybenzothiazole and 2-(4-hydroxyphenyl)-6-methoxybenzothiazole, respectively. The detection limits for aromatic aldehydes in the spectrofluorometric method were 7–80 pmol ml −1 depending on the aldehydes. The fluorescent derivatives of aromatic aldehydes can be separated by reversed-phase chromatography and their detection limits ( S/N = 3) are 0.1–0.4 pmol on column.