Effect of intraperitoneal (IP) injection of naltrexone (Ntx), at a dose ineffective per se (.25 mg/kg), on buprenorphine-induced decreased ethanol intake (3.0 mg/kg) in Marchigian Sardinian alcohol-preferring rats. Five minutes after Ntx administration animals received an IP injection of buprenorphine (Bup), and ethanol was given to the animals 90 min after Bup. Alcohol consumption was monitored at 30, 60, 90, and 120 min. Values represent the mean (± SEM) of eight subjects. Difference from control subjects: *p < .05. Veh, vehicle.