Compounds of the formula (I) ##STR1## in which R.sub.1 and R.sub.2 each may represent hydrogen, alkyl, cycloalkyl, alkenyl, alkynyl, aralkyl, or alkyl, substituted by hydroxy, C.sub.1-3 alkoxy, amino, C.sub.1-3 alkylamino or di-C.sub.1-3 alkylamino or R.sub.1 and R.sub.2 together with the nitrogen atom to which they are attached form an alicyclic heterocyclic ring which may be unsubstituted or may be substituted by one or more C.sub.1-3 alkyl groups or a hydroxy group and/or may contain another heteroatom are described.Alk is a straight lower alkylene chain,Q is a furan or thiophen ring, the furan ring optionally bearing a further substituent R.sub.5 adjacent to the group R.sub.1 R.sub.2 NAlk-- or Q represents a benzene ring.R.sub.5 represents halogen or C.sub.1-3 alkyl which may be substituted by a hydroxy or C.sub.1-3 alkoxy group;X represents --CH.sub.2 --, --O-- or --S--;n represents zero or 1;m represents 2, 3 or 4;Y represents .dbd.O or .dbd.S;R.sub.3 represents hydrogen in which case R.sub.4 represents methyl or R.sub.3 represents --(CH.sub.2).sub.p V(CH.sub.2).sub.q Ar, phenyl, or alkyl in which case R.sub.4 represents hydrogen;V represents --CH.sub.2 --, --O--, or --S--;p represents zero, 1, 2 or 3;q represents zero, 1, 2 or 3;the sum of p+q being 3 or less;Ar represents an aromatic carbocyclic or heterocyclic ring being optionally substituted by at least one C.sub.1-3 alkyl, C.sub.1-3 alkoxy C.sub.1-3 alkyl, hydroxy, C.sub.1-3 alkoxy, methylenedioxy, halogen, trifluoromethyl or di-C.sub.1-3 alkylamino group;except that when n is zero and X is oxygen then Q represents a benzene or thiophen ring. The compounds of formula (I) have pharmacological activity as selective histamine H.sub.2 -antagonists.