In the process for the preparation of 2-substituted 1-(acylaminoalkyl)-2-imidazolines of the general formula I ##STR1## wherein R denotes an alkylene radical and R.sup.1 denotes a fatty acid radical, for example, a fatty acid and a dialkylenetriamine are reacted in a molar ratio of (1.9 to 2.0): 1 in such a way that the dialkylenetriamine is initially introduced hot under an inert gas atmosphere and the fatty acid is metered in hot and the amido amine formation is subsequently completed by heating to temperatures from 140.degree. to 190.degree. C. and the cyclization to the compound of the formula I is subsequently carried out at an under-pressure of at least 50 mbar.