Historically, the major emphasis on the study of purinergic systems has been predominantly in the areas of physiology and gross pharmacology. The last decade has seen an exponential in- crease in the number of publications related to the role of both adenosine and A TP in mammalian tissue function, a level of interest that has evolved from a more molecular focus on the identity of adenosine and A TP receptor subtypes and the search for selective ligands and development of radioligand binding assays by Fred Bruns and colleagues (especially that for A receptors) that played z a highly significant role in advancing research in the area. In the 60 years since adenosine was first shown to be a potent hypotensive agent, a considerable investment has been made by several pharmaceutical companies-including Abbott, Byk Gulden, Takeda, Warner-LambertlParke Davis, Boehringer Mann- heim, Boehringer Ingelheim, Nelson/Whitby Research and CffiA- Geigy-as well as John Daly's laboratory at the National Institutes of Health, to design new adenosine receptor ligands, and both agon- ists and antagonists with the aim of developing new therapeutic entiities.Numerous research tools have derived from these efforts including: 2-chloroadenosine, R-PIA (~-phenylisopropyladeno- sine; NECA (5' N-ethylcarboxamidoadenosine); CV1808; CI936; PD 125,944; ~-benzyladenosine; PACPX; CPX; CPT; XAC; CGS 15943 and CGS 21680. Yet in the realm of therapeutics it was only in 1989 that adenosine itself was approved for human use in the treatment of supraventricular arrythmias.