Summary The influence of caffeine upon avoidance behavior in the rat was studied by administering the drug at the doses of 1, 2 and 20 mg/kg, i.p., 45 min before the acquisition of a single-trial “step-down” task and by testing the animals 24h later. In order to better detect a possible facilitating effect of caffeine, half of the animals of each group was submitted to electroconvulsive shock (ECS) immediately after training. 1 and 2 mg/kg of caffeine given 45 min before training did not influence passive avoidance conditioning of rats not submitted to ECS, whereas 20 mg/kg significantly impaired avoidance behavior. A possible state-dependent learning component for the effect of the highest dose was ruled out by treating animals 45 min before both sessions. ECS-induced amnesia was prevented by 1 mg/kg of caffeine given i.p. 45 min before training, whereas the other doses were ineffective to this regard. Post-trial administrations of 1 and 20 mg/kg of caffeine were without effect both on ECS-induced amnesia and on avoidance behavior of rats not submitted to ECS. Present findings suggest that a low dose of caffeine has a potential facilitating effect upon passive avoidance conditioning which can be revealed when memory processes are impaired by an injuring event like ECS.