This International Standard specifies a method for the determination of exchangeable acidity in barium chloride extracts of soil samples obtained according to ISO 11260. The procedure described herein mainly concerns the determination of total exchangeable acidity by means of a fixed-pH end-point titration (see note). Two optional procedures are also given, describing respectively, determinations of free H+ acidity and of aluminium in the extracts. This International Standard is applicable to all types of air-dry soil samples which have been pretreated in accordance with ISO 11464. NOTE Titration of exchangeable acidity by means of a fixed-pH end-point may not be specific to a given acid species. The endpoint pH value retained is 7,8, corresponding to complete precipitation of Al+3 ions in synthetic solutions. Titration of soil extracts to this pH may also include some more weakly ionized species or weak acid organic compounds.