The purpose of these studies was to determine if ECS is capable of preventing the retention of cocaine-induced conditioned increases in locomotor behavior. One group of rats (paired) was injected with 40 mg/kg of cocaine immediately before a 30 min exposure to a locomotor monitoring chamber while the other group (unpaired) was injected with saline prior to a similar exposure. One hour following return to their home cages, the paired rats were injected with saline while the unpaired animals were injected with 40 mg/kg of cocaine. On day 2, both groups were injected with 10 mg/kg of cocaine and returned to the test apparatus. The presence of conditioned cocaine effects are indicated by enhanced locomotor output in the paired group relative to the unpaired group on day 2. ECS delivered immediately following training on day 1 was effective in preventing the retention of conditioning. ECS delivered 1 h prior to training, 1 h after or 1 h before on day 2 were ineffective. Cocaine-induced conditioning appears to involve associative learning that can be disrupted by ECS delivered immediately following training.