The present invention relates to phenylacetic acid derivatives of the formula I ##STR1## where the substituents and the index have the following meanings: X is NOCH.sub.3, CHOCH.sub.3, CHCH.sub.3 and [sic] CHCH.sub.2 CH.sub.3 ;R.sup.1 is hydrogen and [sic] C.sub.1 -C.sub.4 -alkyl;R.sup.2 is cyano, nitro, trifluoromethyl, halogen, C.sub.1 -C.sub.4 -alkyl and [sic] C.sub.1 -C.sub.4 -alkoxy;m is 0, 1 or 2, it being possible for the R.sup.2 radicals to be different if m is 2;R.sup.3 is hydrogen, cyano, nitro, hydroxyl, amino, halogen, C.sub.1 -C.sub.1 -alkyl, C.sub.1 -C.sub.4 -haloalkyl, C.sub.1 -C.sub.4 -alkoxy, C.sub.1 -C.sub.4 -haloalkoxy, C.sub.1 -C.sub.4 -alkylthio, C.sub.1 -C.sub.4 -alkylamino or di-C.sub.1 -C.sub.4 -alkylamino;R.sup.4 is hydrogen, cyano, nitro, hydroxyl, amino, halogen,R.sup.5 is hydrogen, C.sub.1 -C.sub.10 -alkyl, C.sub.3 -C.sub.6 -cycloalkyl, C.sub.2 -C.sub.10 -alkenyl, C.sub.2 -C.sub.10 -alkynyl, C.sub.1 -C.sub.10 -alkylcarbonyl, C.sub.2 -C.sub.10 -alkenylcarbonyl, C.sub.3 -C.sub.10 -alkynylcarbonyl or C.sub.1 -C.sub.10 -alkylsulfonyl, it being possible for these radicals to be partly or completely halogenated or to carry one to three of the following groups: cyano, nitro, hydroxyl, mercapto, amino, carboxyl, aminocarbonyl, aminothiocarbonyl,