A novel fused bicyclic pyrimidine derivative or a salt thereof that acts as a tachykinin receptor antagonist and, in particular, as an NK1 receptor antagonist is represented by the following general formula (1): ##STR00001## wherein the rings A and B are each a benzene ring having 1 to 3 substituents (any adjacent two of which may be bound to one another to form a ring); the ring C is a nitrogen-containing ring; R is a hydrogen atom, a C.sub.1 to C.sub.6 alkyl group, a C.sub.1 to C.sub.6 alkylcarbonyl group, or a C.sub.1 to C.sub.6 alkylsulfonyl group; m is 1 or 2; and n is 2 or 3.