An amino-acid ester is produced in the form of a salt with a halogen acid in a single operation by heating a lactam with an alcohol in the presence of a gaseous halogen acid and a substantial quantity of water until at least part of the lactam has undergone ring opening, and subsequently removing water from the reaction mixture by distillation. The halogen acid is preferably hydrogen chloride or hydrogen bromide and the water is preferably removed by azeotropic distillation, preferably with benzene or one of its inert substitution derivatives. The lactam and alcohol are preferably heated in the presence of 0,6-1,5 moles of water per mole of lactam and alcohols boiling at 100 DEG C. or above are preferred, several being specified. The free esters may be obtained from their salts by dissolution of the salt in water, neutralisation of the acid with a base, and extraction of the liberated ester with an organic solvent. Examples describe the preparation of the hydrochlorides of: (1) butyl e -aminocaproate; (2) 2-ethylhexyl e -aminocaproate; (3) n-octyl e -aminocaproate; (4) cyclohexyl e -aminocaproate; (5) n-decyl e -aminocaproate; (6) lauryl e -aminocaproate; (7) benzyl e -aminocaproate; (8) ethylene bise -aminocaproate; (9) n-butyl g -aminobutyrate.