Compounds of formula I, ##STR1## in which A is a 5 or 6 membered, fully unsaturated, carbocyclic or heterocyclic ring,B is a 5 or 6 membered, fully unsaturated, nitrogen containing heterocyclic ring,X is NR.sub.19, O or S,R.sub.19 is hydrogen or alkyl optionally substituted by --OCOR,n is 0 or 1,R.sub.3, R.sub.4, R.sub.5, R.sub.6, R.sub.7, R.sub.8, R.sub.9 and R.sub.10 have various significances,R.sub.1 and R.sub.2, are hydrogen or alkyl or together with the ring carbon atoms to which they are attached, form a benzene or pyridine ring, which ring carries substituents R.sub.15, R.sub.16, R.sub.17 and R.sub.18,R.sub.15, R.sub.16, R.sub.17 and R.sub.18, have varioussignificances, with certain provisos are described.Processes for making the compounds and pharmaceutical formulations containing them, e.g. for the treatment of conditions including excess gastric acid secretion, are also described.