The purpose of this study was to improve the reliability of discrimination (or identification) of dyed hair by analyzing chemical substances present in the hair, as an addition to the conventional macroscopical and microscopical examinations and ABO blood group examination. Oxidation hair-dye components such as p-phenylenediamine (PPDA), toluylene-2,5-diamine (T-2,5-DA), o-aminophenol (OAP), m-aminophenol (MAP), p-aminophenol (PAP) and p-amino-o-cresol (PAOC) were selected as the object of study. After alkaline-digestion, hair samples were adjusted to a pH of 12.6 to 12.8, and applied onto an Extrelut column. After 15 min, the components were simultaneously extracted and derivatized with n-hexane including 1% heptafluoro-n-butyryl (HFB) chloride. Their HFB derivatives within a condensed sample were diluted in ethyl acetate, and analyzed by gas chromatography-mass spectrometry (GC-MS) with full mass scanning or selected ion monitoring. For estimating their levels, 2,4,6-trimethylaniline was used as the internal standard. Standard curves obtained by preparing a 5 cm segment of control hair spiked with authentic substances were linear, ranging from 0.1 to 4.0 µg for PPDA and T-2,5-DA, and from 0.01 to 0.4 µg for OAP, MAP, PAP and PAOC. The coefficient of variation of inter-day precisions (each n = 4) was below 16% for PPDA, below 20% for OAP and PAP and below 24% for T-2,5-DA, MAP and PAOC. These components were detectable even at 6 ng for PPDA, T-2,5-DA, MAP and PAP, 8 ng for OAP, and 4 ng for PAOC. Recovery percents using this procedure ranged from 54 to 86%. By using actual dyed hair samples this method was shown to provide high sensitivity for accurate detection.