Compounds of formula I ##STR1## wherein R.sup.1 signifies phenyl, substituted phenyl or heterocyclyl;R.sup.2 signifies phenyl or substituted phenyl;R.sup.3 signifies hydrogen, lower-alkyl, cyano, carboxy, esterified carboxy, phenyl, substituted phenyl, heterocyclyl or a residue --CONR.sup.5 R.sup.6 or --NR.sup.5 COR.sup.7 ;R.sup.4 signifies hydrogen or lower-alkyl;R.sup.5 signifies hydrogen or a residue R.sup.7, andR.sup.6 signifies --(CH.sub.2).sub.m R.sup.7 ; orR.sup.5 and R.sup.6 together with the N atom associated with them signify a heterocyclic residue;R.sup.7 signifies phenyl, substituted phenyl, cycloalkyl, heterocyclyl, lower-alkyl, cyano-lower-alkyl, hydroxy-lower-alkyl, di-lower-alkylamino-lower-alkyl, carboxy-lower-alkyl, lower-alkoxycarbonyl-lower-alkyl, lower-alkoxycarbonylamino-lower-alkyl or phenyl-lower-alkoxycarbonyl;R.sup.a signifies hydrogen, lower-alkyl or hydroxy;R.sup.b signifies hydrogen or lower-alkyl;Z signifies hydroxy, amino or a residue --OR.sup.8, --OC(O)NHR.sup.8, --OC(O)OR.sup.8, --NHC(O)NHR.sup.8 or --NHC(O)OR.sup.8 ;R.sup.8 signifies heterocyclyl, phenyl, substituted phenyl or lower-alkyl;A and Y each independently signify oxygen or sulphur,X signifies nitrogen or CH;m signifies 0, 1 or 2; andn signifies 0, 1 or 2;and pharmaceutically usable salts thereof are inhibitors of endothelin receptors.They can therefore be used for the treatment of disorders which are associated with endothelin activities, especially circulatory disorders such as hypertension, ischaemia, vasospasms and angina pectoris.