A novel process for the preparation of E-2-propyl-2-pentenoic acid and its physiologically compatible salts is described, in which di-n-propyl-ketone-cyanohydrin is used as the starting compound. The compound is either(a) dehydrated with thionyl chloride and the acid nitrile formed is subsequently saponified with a stoichiometric excess of potassium hydroxide, or(b) is initially converted into 2-hydroxy-2-propyl-pentanoic acid and the latter is subsequently dehydrated in the presence of a less than stoichiometric quantity of a tertiary amine at a temperature of at least 200.degree. C.The free acid is optionally converted into the salt form, preferably using the corresponding salts of carbon dioxide in an aqueous acetone solution.