A compound of the general formula I: ##STR1## in which Ar is a pyridyl, quinolinyl, isoquinolinyl, naphthyridinyl, pyrimidyl, quinazolinyl, thiazolyl, benzothiazolyl, imidazolyl, benzimidazolyl, oxazolyl, benzoxazolyl, thienyl, benzothienyl or naphthyl group; optionally substituted with one or more halogen or alkyl, alkyloxy, alkylthio, trifluoromethyl, amino, alkylamino, dialkylamino, hydroxy, cyano, alkylsulphinyl, alkylsulphonyl, sulphamido, alkylsulphamido, dialkylsulphamido, alkylcarbonyl, benzoyl, alkyloxycarbonyl, carboxy, phenoxycarbonyl, alkylcabonyloxy, benzoyloxy, alkylcarbonylamino, benzamido, phenyl, benzyl, phenoxy or phenylthio group, provided that (i) when Ar is a pyridyl group, the pyridyl group must be substituted, (ii) an alkyl moiety contains 1 to 4 straight- or branched chain carbon atoms; (iii) a phenyl moiety may be unsubstituted or substituted with one or more halogen or alkyl, alkyloxy, alkylthio, trifluoromethyl, amino, alkylamino, dialkylamino, hydroxy, cyano, phenyl or benzyl groupin separate enantiomeric form or mixtures thereof, or a pharmaceutically acceptable salt thereof is useful in the treatment of all pathological conditions in which PAF-acether may be implicated directly or indirectly.