Compounds of formula (I), and salt and prodrugs thereof, wherein Q is optionally substituted phenyl or benzhydryl; R.sup.1 is H; optionally substituted C.sub.1-6 alkyl; optionally substituted phenyl(C.sub.1-4 alkyl); C.sub.2-6 alkenyl; C.sub.2-6 alkynyl; COR.sup.a ; COOR.sup.a ; COHet; COC.sub.1-6 alkylhalo; COC.sub.1-6 alkylNR.sup.a R.sup.b ; CONR.sup.12 C.sub.1-6 alkylCONR.sup.a R.sup.b ; CONR.sup.a R.sup.b ; or SO.sub.2 R.sup.a ; R.sup.2 represents H, C.sub.1-6 alkyl or C.sub.2-6 alkenyl; or R.sup.1 and R.sup.2 together form a chain (CH.sub.2).sub.q optionally substituted by oxo where q is 4 or 5 and where one methylene group may optionally be replaced by an oxygen atom or a group NR.sup.x, where R.sup.x is H or C.sub.1-6 alkyl; R.sup.3 is C.sub.1-3 alkyl substituted by optionally substituted phenyl; R.sup.4 and R.sup.5 are each H, C.sub.1-6 alkyl or C.sub.2-6 alkenyl; and Z represents O or S; are tachykinin receptor antagonists useful in therapy.