This invention provides a series of novel heterocyclic carboxamides of formula I in which the group --Y--Z< is selected from --C(Ra).dbd.C<, --N.dbd.C<, and --CH(Ra)--CH< 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 diseasxes, 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.