As it has been reported that the depolarization induced acetylcholine(ACh) release is modulated by activation of presynaptic A₁-adenosine heteroreceptor and various lines of evidence indicate the A₂-receptor is present In hippocampus, this study was undertaken to delineate the role of adenosine receptors on hippocampal ACh release. Slices from the rat hippocampus were equilibrated with [³H]-choline and the release of the labelled product, [³H]-ACh, which evoked by electrical stimulation(3 Hz, 5 Vcm^-1, 2 ms, rectangular pulses) was measured, and the influence of various agents on the evoked tritium outflow was Investigated. Adenosine(0.3 ~ 100μM) and CPA(0.1 ~ 30μM) decreased the [³H]-ACh release in a dose-dependent manner without changing the basal rate of release. DPCPX(1 ~ 10μM), a selective A₁-receptor, antagonist, increased the [³H]-ACh release in a dose related fashion with slight increase of basal tritium release. And the effects of adenosine and CPA were significantly inhibited by DPCPX(2μM) treatment. CPCA, a specific A₂-agonist, in concentration ranging from 0.3 to 30 μM, decreased the evoked tritium outflow, and these effects were also abolished by DPCPX(2μM) treatment. But the CPCA effects were not affected by DMPX(2μM), a specific Aa-antagonist, treatment. However, CGS 21680c, a recently introduced potent A₂-agonist, in concentration ranging from 0.1 to 10μM, did not alter the evoked tritium outflow. These results indicate that the decrement of the evoked ACh release by adenosine is mediated by A₁-heteroreceptor, but A₂-adenosine receptor is not involved in ACh release in the rat hippocampus.