Abstract: The invention concerns a bicyclic heterocyclic compound of the formula I ##STR1## wherein Q is an optionally substituted 10-membered bicyclic heterocyclic moiety containing 1 or 2 N's and a further O or S heteroatom;A.sup.1 is a direct link to X.sup.1 or (1-3C)alkylene;X.sup.1 is oxy, thio, sulphinyl, sulphonyl or imino;Ar is optionally substituted phenylene or pyridylene;R.sup.1 is (1-4C)alkyl, (3-4C)alkenyl or (3-4C)alkynyl; andR.sup.2 and R.sup.3 together form a group of the formula --A.sup.2 --X.sup.2 --A.sup.3 -- which,together with the carbon atom to which A.sup.2 and A.sup.3 are attached, defines a ring having 5 to 7 ring atoms, wherein each of A.sup.2 and A.sup.3 is (1-3C)alkylene and X.sup.2 is oxy, thio, sulphinyl or sulphonyl; or a pharmaceutically-acceptable salt thereof.The compounds of the invention are inhibitors of the enzyme 5-lipoxygenase.