A pharmaceutically acceptable salt of perindopril of formula (I) is made from a protected precursor compound of formula (II) wherein R represents a carboxyl protecting group, which process comprises subjecting a compound of formula (II) to deprotection of the carboxylic group COOR attached to the heterocyclic ring so as to yield the corresponding free acid, which deprotection is carried out in the presence of a base which forms a pharmaceutically acceptable salt with the free acid formed by the deprotection ##STR00001##