A set of 2-aryl-9-H or methyl-6-morpholinopurine derivatives were synthesized and assayed through radioligand binding tests at human A<inf>1</inf>, A<inf>2A</inf>, A<inf>2B</inf>, and A<inf>3</inf> adenosine receptor subtypes. Eleven purines showed potent antagonism at A<inf>1</inf>, A<inf>3</inf>, dual A<inf>1</inf>/A<inf>2A</inf>, A<inf>1</inf>/A<inf>2B</inf>, or A<inf>1</inf>/A<inf>3</inf> adenosine receptor...