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Concurrent use of alcohol and other drugs is a serious problem. Cocaine is the most frequently abused drug overseas. An increasing number of cases demonstrating concurrent use of alcohol and cocaine is being noted. Alcohol preference (AP) in animals is an index of human drinking behavior. In this study brain monoamine and alcohol metabolism were studied to clarify the mechanisms of changes in AP following single or repeated cocaine administration. To inbred strain of mouse, C57BL/6J, 10% alcohol and tap water were given and AP was measured following intraperitoneal cocaine administration once or repeatedly for one week. Then the rate of blood alcohol disappearance in vivo (beta value) and liver alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH) activity in vitro were measured. Changes in brain norepinephrine, dopamine, serotonin and their metabolites were also measured. A single cocaine administration reduced the AP of C57BL/6J mice. beta value was not changed after pretreatment with cocaine. The level of brain dopamine was increased only two hours after cocaine administration. In repeated cocaine administration, AP was reduced after cocaine administration. Brain monoamine levels were not changed. Neither the beta value nor liver ADH, ALDH activity was changed after either single or repeated cocaine administration. It is speculated that reduced AP is associated with an increase in brain dopamine and changes in AP did not contribute to alcohol metabolism pharmacologically. Dopaminergic system makes a rule of, in part, alcohol drinking behavior.