Polyoxyalkylene compounds having at least four oxyalkylene units and one or two terminal hydroxyl groups are etherified by reacting same with organic primary chlorides or bromides in the presence of an aqueous, at least 30% by weight solution of sodium or potassium hydroxide to produce the corresponding etherified polyoxyalkylene derivatives. The molar ratio of the organohalide to the hydroxyl group(s) of the polyoxyalkylene compound is at least 1.2, and the molar ratio of the alkali metal hydroxide to such hydroxyl group(s) is at least 1.