Abstract: A process for the preparation of a dihalogenovinylcyclopropanecarboxylic acid or an ester thereof, of the formula ##STR1## in which Hal each independently is fluorine, chlorine or bromine,R.sup.1 and R.sup.2 each independently is hydrogen or C.sub.1-4 -alkyl, or R.sup.1 and R.sup.2 together with the adjacent carbon atom form a cycloaliphatic ring with up to 7 carbon atoms, andR.sup.3 is hydrogen, C.sub.1-4 -alkyl or optionally substituted arylmethyl or hetero-arylmethyl,which comprises reacting a 3-chloro-2-(2',2'-dihalovinyl)propanecarboxylic acid ester of the formula ##STR2## in which R.sup.4 is C.sub.1-4 -alkyl or optionally substituted arylmethyl or hetero-arylmethyl,with a base. The propane carboxylic acid esters are new and may be formed in situ by reacting a 3-(2',2'-dihalovinyl)-.gamma.-butyrolactone of the formula ##STR3## with a chlorinating agent and then with an alcohol of the formula R.sup.4 --OH.