Using molecular modeling, adenosine receptor ligands were fitted together to maximize correlations between the three most important factors controlling binding to the receptor, namely steric, hydrophobic, and electrostatic complimentarily. Structure-activity relationships can be explained by three binding domains on the receptors. These are hydrophobic, aromatic, and ribose binding domains. We propose that the N6, C2, and C8 hydrophobic binding domains are not discreet but occupy the same region of the receptor.