A method of alleviating a fibrotic disease selected from lung fibrosis and liver cirrhosis in a warm blooded animal, which comprises administering an effective amount of at least one compound having the formula (I) ##STR1## in which X stands for the oxygen or sulphur atom or for the imino (--NH--) or sulphonyl (--SO.sub.2 --) radical, Y stands for a direct linkage, or for the oxygen or sulphur atom or for the sulphonyl (--SO.sub.2 --) radical or for the radical of the formula --CR.sup.1 R.sup.2 --, wherein R.sup.1 and R.sup.2 which may be the same or different are hydrogen, alkyl or aryl radicals or R.sup.1 and R.sup.2 may be joined together to form a cycloalkyl ring, n is an integer having the value 0 or 1, provided that when n is 0, Y stands for the oxygen or sulphur atom or for the sulphonyl (--SO.sub.2 --) radical, or an ester, amide or salt thereof.