Alkaline earth metal salts of ether carboxylic acids corresponding to the following general formula[RO--(C.sub.m H.sub.2m O).sub.n --CH.sub.2 --COO.sup.- ].sub.x M.sup.2+(I)in which R represents C.sub.1 -C.sub.22 alkyl, C.sub.3 -C.sub.22 alkenyl, phenyl, alkylphenyl containing 1 to 3 C.sub.1 -C.sub.15 alkyl radicals, benzyl or phenylethyl, M represents Ca, Sr or Ba, m is equal to 2 or 3, n is equal to 1 to 20 and x is equal to 2; or R is a group of the formula --CH.sub.2 --COO.sup.-, x is equal to 1 and M, m and n are as defined above, are used as catalysts for the ethoxylation or propoxylation of organic compounds containing active H atoms. They afford advantages by virtue of the solubility of the catalysts in the reaction medium and provide for a narrow homolog distribution of the polyalkoxylation products.