The invention relates to N-acyl-N-heterocyclylalkylamino acids of the formula ##STR1## wherein Y.sub.1 is O, S or N(R) and R is hydrogen or C.sub.1 -C.sub.7 alkyl; X.sub.1 is --CO-- or --S(O).sub.m -- and the index m is 0, 1 or 2; one of the variables X.sub.2 and X.sub.4 is C.sub.1 -C.sub.4 alkylene and the other of the variables X.sub.2 and X.sub.4 is a bond; or each of the variables X.sub.2 and X.sub.4 is a bond; X.sub.3 is C.sub.3 -C.sub.7 cycloalkylidene or the structural element --C(X.sub.a)(X.sub.b)-- and X.sub.a is hydrogen or C.sub.1 -C.sub.7 alkyl and X.sub.b is C.sub.1 -C.sub.7 alkyl; and the rings A, B and C, with the exception of the substituents indicated in the formula, and also aromatic substituents are, independently of one another, unsubstituted or mono- or poly-substituted by substituents selected from the group consisting of halogen, C.sub.1 -C.sub.7 alkyl, C.sub.1 -C.sub.7 alkoxy, C.sub.2 -C.sub.7 alkenyloxy, phenoxy, benzyloxy, trifluoromethyl and S(O).sub.m --R, wherein m is 0, 1 or 2 and R is hydrogen or C.sub.1 -C.sub.7 alkyl; or a salt thereof.