A 3-substituted 3,4,5,6,7,8-hexahydropyrido[4',3':4,5]thieno[2,3-d]pyrimidine compound of formula I ##STR1## wherein R.sup.1 is hydrogen, C.sub.1 -C.sub.4 -alkyl, acetyl or benzoyl, optionally substituted phenyl-C.sub.1 -C.sub.4 -alkyl, naphthyl-C.sub.1 -C.sub.3 -alkyl, phenyl-C.sub.2 -C.sub.3 -alkanone or a phenylcarbamoyl-C.sub.2 -alkyl, R.sup.2 is optionally substituted phenyl, pyridyl, pyrimidyl or pyrazinyl, or an optionally substituted bicyclus wherein one of the two fused rings is a phenyl, a pyridyl, a pyrimidyl or a pyrazinyl ring, A is NH or oxygen, B is hydrogen or methyl, C is hydrogen, methyl or hydroxyl, X is nitrogen, Y is CH.sub.2, CH.sub.2 --C.sub.2, CH.sub.2 --C.sub.2 --CH.sub.2 or CH.sub.2 --CH, Z is nitrogen, C or CH, and the linkage between Y and Z is a single or a double bond, and n is 2, 3 or 4, or a physiologically tolerated salt thereof, and compositions comprising them and their use as antagonists of 5HT.sub.1B and 5HT.sub.1A and for the treatment of depression and related disorders.