Acetaldehyde (ACD), the first metabolite of ethanol (EtOH) appears to be involved in many of the psychoactive effects of its parent compound, including EtOH-induced activation of the mesolimbic dopamine (DA) system, thereby suggesting that ACD may participate in EtOH motivational properties. l-cysteine (Lcys), a thiol compound sequestering ACD, is able to prevent the behavioral effect of EtOH and ACD. Here we show that the stimulatory effect of both EtOH and ACD on the mesolimbic DA system is prevented by Lcys pretreatment.Male Wistar rats were implanted with a microdialysis probe in the nucleus accumbens shell (NAccs), and pretreated intraperitoneally with Lcys (30 mg/kg) before intragastric administration of EtOH (1 g/kg) or ACD (20 mg/kg) or before intraperitoneal administration of morphine (2.5 mg/kg). Pretreatment with Lcys prevented both EtOH and ACD-induced DA release in the NAccs without influencing morphine-induced DA release, suggesting that Lcys specifically affects EtOH-induced DA release possibly through ACD sequestering.Our results underscore the role of ACD on EtOH-induced stimulation of DA mesoaccumbens system and support the notion that thiol compounds such as Lcys, by modulating EtOH-derived ACD bioavailability, would blunt EtOH rewarding properties.