This invention provides a series of novel heterocyclic aliphatic carboxamides of formula I in which the group >Z--Y--X< is selected from >C.dbd.CH--N<, >N--CH.dbd.C<, >C.dbd.N--N< and >N--N.dbd.C< and the other radicals have the meanings defined in the following specification. The compounds of formula I are leukotriene antagonists. The invention also provides pharmaceutically acceptable salts of the formula I compounds; pharmaceutical compositions containing the formula I compound, or their salts, for use in the treatment of, for example, allergic or inflammatory diseases, or endotoxic or traumatic shock conditions; and processes for the manufacture of the formula I compounds, as well as intermediates for use in such manufacture.