Abstract: Compounds of formula I ##STR1## in which R.sub.1 and R.sub.2, which may be the same or different, are hydrogen, a C.sub.1 to C.sub.3 alkyl group or R.sub.1 and R.sub.2 together with the nitrogen to which they are attached form an optionally substituted heterocyclic ring; R.sub.3 and R.sub.4, which may be the same or different are hydrogen, a C.sub.1 to C.sub.3 alkyl or an optionally substituted C.sub.3 to C.sub.6 cycloalkyl group, or R.sub.3 and R.sub.4 together with the nitrogen to which they are attached form an optionally substituted heterocyclic ring; m is 0, 1 or 2; p is 0, 1 or 2; E is an alkylene group connected to or interrupted by an oxygen or a sulphur atom; J is hydrogen or a substituent group; and their pharmaceutically acceptable salts have utility as histamine H.sub.2 -receptor antagonists.