Owing to the similarity in the properties of pairs of dyes made by coupling diazotised 4‐chloro‐2‐aminophenol‐5‐ and ‐6‐sulphonic acids with the same coupling component, the identity of the former compound was open to suspicion. Consequently, 4‐chloro‐2‐aminophenol‐5‐sulphonic acid has been prepared by sulphonating 5‐chlorobenzoxazolone and then hydrolysing the 5‐chloro‐benzoxazolone‐6‐Bulphonic acid. 4‐Chloro‐2‐aminophenol‐5‐ and 6‐sulphonic acids have been characterised by conversion into 5‐chlorobenzoxazolone‐6‐ and ‐7‐sulphonic acids, from which theS‐benzylthiuronium andp‐toluidine salts were prepared. These derivatives possess satisfactory melting points and are suitable for the identification of 4‐chloro‐2‐aminophenol‐5‐ and ‐6‐sulphonic acids. The preparation of 2‐amino‐phenol‐5‐sulphonic acid fromo‐aminophenolviabenzoxazolono is described, and 2‐aminophenol‐4‐ and ‐5‐sulphon