Following the determination of total exchangeable acidity, exchangeable aluminium can be determined from the release of hydroxyl ions (OH‐) by NaF if all the aluminium has been neutralised to Al(OH),. The released hydroxyl was measured by titration to a phenolphthalein endpoint and to an isoelectric endpoint. When compared with a colorimetric procedure for Al, both titrimetric methods gave inaccurate and unreliable results for solutions containing known amounts of Al. A colorimetric method using Alizarin Red S is recommended.