Adenosine is a depressant in the central nervous system with pre‐ and postsynaptic effects. In the present study, intracellular recording techniques were applied to investigate the modulatory effects of adenosine on projection neurons in the lateral rat amygdala (LA), maintained as slices in vitro. Adenosine reversibly reduced the amplitude of a fast inhibitory postsynaptic potential (IPSP) that was evoked by electrical stimulation of the external capsule and pharmacologically isolated by applying an N‐methyl‐D‐aspartate and non‐N‐methyl‐D‐aspartate receptor antagonist, DL‐(−)‐2‐amino‐5‐methyl‐4‐isoxazolepropionic acid and 6,7‐Dinitroquinoxaline‐2,3‐dione, respectively, and the γ‐aminobutyric acidB (GABAB) receptor antagonist CGP 35348. The postsynaptic potential that remained was abolished by locally applying bicuculline. Adenosine reduced the amplitude of the fast IPSP on average by 40.3%. It had no significant effect on responses to exogenously applied GABA, on membrane potential or on input resistance, suggesting that the site of action was at presynaptic inhibitory interneurons in the LA. The response to adenosine was mimicked by the selective adenosine A1 receptor agonist N6‐cyclohexyladenosine and blocked by the selective adenosine A1 receptor antagonist 8‐cyclopentyl‐1,3‐dipropylxanthine. Neuronal responsiveness in the amygdala is largely controlled by inhibitory processes. Adenosine can presynaptically downregulate inhibitory postsynaptic responses and could exert dampening effects likely by depression of both excitatory and inhibitory neurotransmitter release. British Journal of Pharmacology (1999) 128, 190–196; doi:10.1038/sj.bjp.0702761