A compound of the general formula I; STR1 in which R is hydrogen or a halogen or an alkyl, alkyloxy, alkylthio, trifluoromethyl, amino, alkylamino, dialkylamino, hydroxy, cyano, carboxy, alkylsulphinyl, alkylsulphonyl, sulphamido, alkylsulphamido, dialkylsulphamido, carbamoyl, alkylcarbamoyl, dialkylcarbamoyl, phenylcarbamoyl, diphenylcarbamoyl, pyridylcarbamoyl, dipyridylcarbamoyl, benzyl, alkylcarbonyl, benzoyl, alkyloxycarbonyl, phenoxycarbonyl, alkylcarbonyloxy, benzoyloxy, alkylcarbonylamino, benzamido, phenyl, phenoxy or phenylthio group, X is oxygen or sulphur or an imino, alkylimino, phenylimino, benzylimino, sulphinyl, sulphonyl, carbonyl, carbonylmethylene, methylenecarbonyl, carbonylvinylene or vinylenecarbonyl group, or X represents a valency bond or a straight-chain alkylene group containing 1 to 4 carbon atoms and Ar is a phenyl, naphthyl, pyridyl, quinolinyl, isoquinolinyl, thienyl, benzothienyl, thieno 3,2-b!thien-2-yl or thieno 2,3-b!thien-2-yl group, it being possible for the group Ar to be unsubstituted or substituted with one or more halogen or alkyl, alkyloxy, alkylthio, trifluoromethyl, amino, alkylamino, dialkylamino, hydroxy, cyano, carboxy, alkylsulphinyl, alkylsulphonyl, sulphamido, alkylsulphamido, dialkylsulphamido, carbamoyl, alkylcarbamoyl, dialkylcarbamoyl, phenylcarbamoyl, diphenylcarbamoyl, pyridylcarbamoyl, dipyridylcarbamoyl, benzyl, alkylcarbonyl, benzoyl, alkyloxycarbonyl, phenoxycarbonyl, alkylcarbonyloxy, benzoyloxy, alkylcarbonylamino or benzamido group;each alkyl moiety containing 1 to 4 straight-or branched-chain carbon atoms; the compound being in separate enantiomeric form or mixtures thereof or a pharmaceutically acceptable salt thereof is useful in the treatment of all the pathological conditions in which PAF-acether may be directly or indirectly implicated.