A set of 2-aryl-9-H or methyl-6-morpholinopurine derivatives were synthesized and assayed through radioligand binding tests at human A₁, A_2A, A_2B, and A₃ adenosine receptor subtypes. Eleven purines showed potent antagonism at A₁, A₃, dual A₁/A_2A, A₁/A_2B, or A₁/A₃ adenosine receptors. Additionally, three compounds showed high affinity without selectivity for any specific adenosine receptor. The structure-activity relationships were made for this group of new compounds. The 9-methylpurine derivatives were generally less potent but more selective, and the 9H-purine derivatives were more potent but less selective. These compounds can be an important source of new biochemical tools and/or pharmacological drugs.