Adenosine, inosine, hypoxanthine and guanosine were measured in perfusates collected from the right and left striatum of halothane-anaesthetized naive and 6-hydroxydopamine-denervated rats by using microdialysis. Samples were taken under basal and KCl-stimulated conditions. Dopamine, dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA) and 5-hydroxyindoleacetic acid (5-HIAA) were simultaneously measured. Purines and monoamines were assayed by HPLC-UV and HPLC-EC respectively. In naive rats, basal adenosine (1 microM), inosine (2 microM), hypoxanthine (4 microM), guanosine (0.5 microM) and dopamine (DA, 0.02 microM) levels (corrected by using the in vitro % recovery of each probe) were increased by the inclusion of 100 mM of KCl into the perfusion medium (2.5-, 3-, 3.5-, 1.5- and 30-fold, respectively, while DOPAC (6 microM), HVA (5 microM) and 5-HIAA (3 microM) levels were (72%, 68% and 45% respectively). DA was strongly diminished in the denervated striatum, but when detectable, could be increased (1- to 12-fold) by KCl stimulation. Adenosine, inosine, hypoxanthine and guanosine were, however, largely unaffected by the DA denervation and could be enhanced by KCl stimulation (2-, 3-, 4- and 1.5-fold respectively). The present results indicate that: (1) as in the case for DA, there is a pool of striatal adenosine which is releasable by high concentrations of extracellular K+; however, (2) this pool of adenosine seems not to be significantly modified by mesencephalic dopamine deafferentation.