The invention concerns novel compounds of formula I X--A--S--Y (I) wherein X is a radical selected from imidazolyl, pyridyl, quinolyl, tetrahydropyridyl or piperidyl any of which may be substituted and Y is any of the above radicals or a pyridinium radical, A is alkylene of 1-6 carbon atoms. Most of the compounds are anti-ulcer agents but some have anti-hypertensive activity, eg where X is quinolyl. Methods of treating ulcers and anti-ulcer compositions are also described.