Abstract A series of 2-[2-(5-dimethylaminomethyl-2-furanylmethylthio) ethylamino]-4- pyrimidones is described containing a variety of substituents in the 5-position of the pyrimidone (isocytosine) ring. Good H 2-receptor histamine antagonist activity is retained over a range of basic and neutral, polar and non-polar substituents and the majority of compounds are selective for the H 2-receptor. Modifications have also been made to the ...