Abstract: The invention concerns a cyclic ether derivative of the formula I, ##STR1## wherein Ar.sup.1 is optionally substituted phenyl or naphthyl;A.sup.1 is (1-6C)alkylene, (3-6C)alkenylene, (3-6C)alkynylene or cyclo(3-6C)alkylene;Ar.sup.2 is optionally substituted phenylene, or a 6 membered heterocyclene moiety containing up to three nitrogen atoms;R.sup.1 and R.sup.2 together form a group of the formula --A.sup.2 --X--A.sup.3 -- wherein each of A.sup.2 and A.sup.3 is (1-6C)alkylene and X is oxy, thio, sulphinyl, sulphonyl or imino; andR.sup.3 is (1-6C)alkyl, (2-6C)alkenyl, (2-6C)alkynyl or substituted (1-4C)alkyl;or a pharmaceutically-acceptable salt thereof.The compounds of the invention are inhibitors of the enzyme 5-lipoxygenase.