Herbicidal N-isopropylheteroaryloxyacetanilides of the formula ##STR1## in which A stands for nitrogen or the group C-R.sup.3 whereR.sup.3 stands for halogen, cyano, alkyl, halogenoalkyl, alkoxy, halogenoalkoxy, alkylthio, halogenoalkylthio, alkylsulphinyl or alkylsulphonyl,B stands for nitrogen or the group C-R.sup.4 l whereR.sup.4 stands for halogen, cyano, alkyl, halogenoalkyl, alkoxy, halogenoalkoxy, alkylthio, halogenolakylthio, alkylsulphinyl, halogenoalkylsulphinyl, alkylsulphonyl, halogenoalkylsulphonyl, for phenyl which is optionally substituted by halogen, alkyl, halogenoalkyl, alkoxy or halogenoalkoxy, or for the group -CY.sub.2 -Z-R.sup.5 whereR.sup.5 stands for alkyl, which is optionally substituted by halogen, alkoxy or alkylthio, or for phenyl which is optionally substituted by halogen, alkyl, halogenoalkyl, alkoxy, halogenoalkoxy, alkylthio or halogenoalkylthio,Y stands for hydrogen or halogen,Z stands for oxygen, sulphur, SO or SO.sub.2,R.sup.1 stands for hydrogen, halogen, cyano, nitro, alkyl, halogenoalkyl, alkoxy, halogenoalkoxy, alkylthio or halogenoalkylthio,R.sup.2 stands for hydrogen, halogen, alkyl, halogenoalkyl or alkoxy andX stands for oxygen or sulphur,excluding the compound N-isopropyl-(5-trifluoromethyl-1,3,4-thiadiazol-2-yl)-oxyacetanilide.