The effect of several adenosine analogues on cyclic AMP accumulation was examined in the rat phaeochromocytoma cell PC12 and in the human T-cell leukaemia cell Jurkat, selected as prototypes of cells predominantly expressing adenosine A2A or A2B receptors. Using the reverse transcription-polymerase chain reaction it was, however, demonstrated that the Jurkat cell and the PC12 cell express both A2A and A2B receptor mRNA, albeit in different relative proportions. In PC12 cells the concentration required for half-maximal response (EC50) for the full agonist 5'-N-ethyl-carboxamidoadenosine (NECA) was 30 times lower than in Jurkat cells. There was no significant difference in the pA2 for the antagonist 5-amino-9-chloro-2-(2-furanyl)- 1,2,4-triazolo(1,5-C)quinazolinemonomethanesulphonate (CGS 15943) between the two cell types. In the presence of forskolin (1 microM in PC12 cells; 10 microM in Jurkat cells) the EC50 value for NECA was reduced two-to sixfold. Forskolin also increased the maximal cAMP accumulation twofold in PC12 cells and sevenfold in Jurkat cells. A series of 2-substituted adenosine analogues CV 1808 (2-phenylamino adenosine), CV 1674 [2-(4-methoxyphenyl)adenosine], CGS 21680 ¿2-[p-(2-carbonylethyl)phenylethylamino]-5'-N-ethyl- carboxamido adenosine¿, and four 2-substituted isoguanosines, SHA 40 [2-(2-phenylethoxy)adenosine; PEA], SHA 91 [2-(2-cyclohexylethoxy)adenosine; CEA], SHA 118 ¿2-[2-(p-methylphenyl)ethoxy]adenosine; MPEA¿, and SHA 125 (2-hexyloxyadenosine; HOA), all raised cAMP accumulation in PC12 cells, but had minimal or no effect in Jurkat cells. In the PC12 cells the addition of forskolin (1 microM) reduced the EC50 by a factor of 2(CV 1808) to 12 (SHA 125). In Jurkat cells all the analogues gave a significant, but submaximal, cAMP response in the presence of forskolin (10 microM), but they were essentially inactive in its absence. The results show that a series of 2-substituted adenosine analogues can be used to discriminate between A2A and A2B receptors. The two receptor subtypes appear to coexist, even in clonal cells selected for typical pharmacology. A2 receptor pharmacology can therefore be complex.